Biomedical subjects

G D Luk

Publications and source records attributed to G D Luk.

At least 55 records · Page 3Linked to original sources

PubMed1990

Aging and intestinal polyamine metabolism in the rat.

Hyperproliferation and delayed expression of enzyme activity occur in small intestinal enterocytes of aging rats, and starvation and refeeding result in impaired control of these processes. Since altered polyamine metabolism may accompany changes in enterocyte proliferation, we studied the effects of nutrient manipulation upon cell numbers, ornithine decarboxylase (ODC) activity and polyamine content in jejunum and ileum of 4- to 5- and 26- to 27-month Fischer rats. In both groups, cell numbers fell during starvation and and increased during refeeding. Crypt cell hyperplasia was found in aging animals. Jejunal putrescine, spermine and spermidine content were greater in older rats, fell during starvation, and rose during refeeding. Ileal ODC activity was 66% greater in the aging rats, but jejunal ODC activity was modestly increased in young animals. Intestinal polyamine content correlates with proliferative changes and polyamine metabolism responds appropriately to nutrient manipulation during aging. Dissociation of ODC activity and polyamine content in aging jejunum probably occurred because enterocyte differentiation was delayed. Investigation of intestinal polyamine metabolism may be useful in elucidating deranged proliferative activities found in the intestine of aging rodents.

Age Factors↗

PubMed1990

Polyamines in intestinal growth.

The total cellular mass of the small intestine is well controlled and can adapt, with hypo- or hyperplasia, to a wide variety of stimuli. Luminal nutrients, hormonal factors and pancreatic and biliary secretions have all been implicated in the regulation of intestinal mucosal growth. The polyamines (putrescine, spermidine and spermine) and the key enzyme controlling their synthesis (ornithine decarboxylase. ODC) are critical for many cell growth processes and appear to play important roles in intestinal growth. During intestinal adaptation in response to jejunectomy, lactation. pancreatic-biliary diversion, starvation-refeeding and feeding with kidney bean lectin, intestinal contents of ODC and polyamines are increased, paralleling increases in mucosal proliferative indices and DNA synthesis. With administration of the specific inhibitor of ODC (difluoromethylornithine, DFMO) the increase in ODC and polyamines is inhibited and intestinal growth is suppressed. In addition, the oral administration of exogenous polyamines results in precocious maturation of the neonatal rat intestine. These results suggest that the polyamines are important for intestinal growth.

Adaptation, Physiological↗

PubMed1990

Cellular levels of thymosin immunoreactive peptides are linked to proliferative events: evidence for a nuclear site of action.

Thymosin alpha 1 (T alpha 1), the N-terminal 28-amino acid fragment of prothymosin alpha (ProT alpha), and ProT alpha, although originally isolated from whole thymus extracts, are also present in nonthymic cells and tissues. We used an ELISA with an antibody raised against T alpha 1 to investigate the relationship between intracellular levels of thymosin immunoreactive peptide(s) (TIP) and cell proliferation in a rat small intestinal IEC-6 cell line. Increasing TIP levels were observed during cell proliferation, which decreased when proliferation was halted by cellular contact inhibition. Serum feeding of cells previously rendered quiescent by serum starvation resulted in a significant increase in TIP within 1 hr. Conversely, serum starvation decreased TIP levels within 1 hr. Peak TIP levels appeared after 3 hr of serum incubation, while maximum [3H]thymidine incorporation was noted after 9 hr, suggesting maximum TIP concentrations in the G1 phase of the proliferative cycle. Immunoelectron microscopy demonstrated an association of TIP with condensed nuclear chromatin. These results support a relation of intracellular TIP levels to IEC-6 cell proliferation and also a nuclear site of action. HPLC analysis of cellular homogenates from proliferating IEC-6 cells revealed a peak of immune reactivity that elutes in the position of T alpha 1.

Animals↗

PubMed1990

Diacetylputrescine and its analog suppress c-myc expression and activation of human B-lymphocytes.

Our studies demonstrate that diacetylputrescine (TMBA), and its analog hexamethylenebisacetamide, HMBA, inhibit the expression of the c-myc oncogene in activated human B-lymphocytes. Activation of human B-cells induced by anti-IgM is associated with the induction of c-myc by greater than 20 times basal levels, maximal levels occurring at about 2 hours. This increased c-myc expression is inhibited by greater than 90% by 3 mM TMBA or 3mM HMBA. TMBA and HMBA also inhibit by greater than 90% the subsequent activation of the B-cells. These diacetylated polyamines may play a regulatory role in B-cell activation.

Acetamides↗

PubMed1989

Attenuation of azoxymethane-induced colonic mucosal ornithine decarboxylase and tyrosine kinase activity by calcium in rats.

Two in vivo and one in vitro studies were performed to evaluate the chemoprotective role of calcium during the early period of azoxymethane (AOM) induction. In the first set of experiments, groups of male Fischer 344 rats were s.c. injected with either AOM (20 mg/kg) or water (controls) and sacrificed immediately (0 time), and 1, 3, 5, and 7 days postinjection. In the second set of experiments, animals were injected with the same dose of AOM and subsequently pair-fed with rat chow containing either calcium carbonate or diet devoid of added calcium. The amount of calcium consumed was calculated to be 250 mg/kg b.w. In both experiments, colonic mucosa was assayed for ornithine decarboxylase (ODC). In addition, tyrosine kinase (Tyr-k) activity as well as tyrosine specific phosphorylation of membrane proteins were determined. Results revealed that maximal stimulation by AOM of ODC and Tyr-k activity occurred 5 days postinjection. This stimulation was significantly suppressed by calcium. AOM also produced an increase in the rate of tyrosine specific phosphorylation of two distinct colonic mucosal membrane proteins with Mr of 57,000 and 59,000. Again, dietary calcium suppressed the stimulation. In the third set of experiments, organ culture was utilized. Methylazoxymethanol, the active metabolite of AOM, was used instead of AOM in this part of the study. Four hour exposure of mucosal explants to methylazoxymethanol (1 microgram/ml) resulted in a significant (20-30%) increase in ODC and Tyr-k activity when compared to controls. Addition of either CaCl2 (2 mumol/ml) or difluoromethylornithine (2 nmol/ml) the irreversible inhibitor of ODC, significantly suppressed the methylazoxymethanol-induced activity of both ODC and Tyr-k. We conclude that calcium may have a chemoprotective role and tyrosine kinases may have a regulatory role in the early stages of AOM induction of colon cancer.

Animals↗

PubMed1989

Biochemical changes in the gastric mucosa after injury in young and aged rats.

Changes in gastric mucosal thymidine kinase (TK) activity (an indicator of proliferative activity) were examined in young (4 month) and aged (24 month) Fischer-344 male rats 6 h after intragastric administration of either 2 M NaCl (1 ml/130 g b.w.) or an equivalent volume of water (control). These changes were related to the expression of c-myc gene, tyrosine kinase (Tyr-K) activity and tyrosine-specific phosphorylation of proteins in the gastric mucosa. Basal gastric mucosal TK activity (data from the controls) in the aged rats was found to be 75% (P less than 0.001) above the young animals. This was accompanied by increased expression of c-myc gene and a 67% (P less than 0.001) enhancement in Tyr-K activity. Intragastric administration of 2 M NaCl resulted in gastric mucosal damage (as evidenced by lesions index) in both age groups. However, in aged rats, the lesions index was found to be about 75% higher than in their younger counterparts. In young rats, mucosal injury resulted in a 95% rise in TK activity, whereas in aged rats it was increased by only 38%, when compared with corresponding controls. This 2-fold rise in TK activity in young rats was also associated with increased expression of the c-myc gene. In young rats, administration of hypertonic saline caused a 90% (P less than 0.001) increment in Tyr-K activity and significantly stimulated tyrosine-specific phosphorylation of five mucosal proteins with an apparent molecular mass of 170, 120, 100, 55 and 43 kDa. On the other hand, administration of hypertonic saline to the aged rats caused only a small 16% (P less than 0.025) increase in Tyr-K activity, and produced no apparent change in either expression of c-myc gene or tyrosine-specific phosphorylation of any of the proteins in the gastric mucosa, when compared with the corresponding controls. We conclude that aging increases the susceptibility of the gastric mucosa to damaging agents and diminishes its regenerative capacity. We also suggest that Tyr-K may play a role in determining these events.

Aging↗

PubMed1989

Abnormal methylation of the calcitonin gene in human colonic neoplasms.

Earlier studies of the methylation status of total genomic DNA and of specific genes have demonstrated, predominantly, hypomethylation in human neoplasms. However, we have recently documented the presence of new sites of methylation in the calcitonin gene in human lymphomas (100%), small cell lung carcinomas (92%), and acute myeloid leukemias (95%). We now report that these same novel calcitonin gene methylation sites are also a feature of DNA from human colonic adenomas (13 out of 14 studied), colon carcinomas (4/13), and established colon carcinoma cell lines (18/19), despite the presence of overall genomic DNA hypomethylation in these neoplasms. The data provide further evidence that regional increases in DNA methylation, like gene hypomethylation, occur in benign colonic neoplasms prior to malignant transformation. The fact that abnormalities of calcitonin gene methylation are less frequent in DNA from human colonic carcinomas than from adenomas and colon carcinoma cell culture lines is of special interest. This finding suggests that a more heterogeneous population of cells is present in the carcinomas and that the calcitonin gene hypermethylation may be inherent to cells which are initially selected for growth in culture or are capable of prolonged survival under culture conditions.

Adenoma↗

PubMed1989

Modulation of epidermal growth factor-induced cell proliferation and receptor binding by insulin in cultured intestinal epithelial cells.

The effect of insulin on EGF-induced cell proliferation and on modulation of EGF receptors was examined in IEC-6 cells in culture. Insulin-induced cell proliferation was not seen until concentration of the hormone reached the microgram (10 micrograms/ml) level, producing an increase in EGF receptor binding affinity (Ka 8.2 +/- .05 x 10(9)M-1 to 1.25 +/- .05 10(10) M-1). In the presence of supraphysiologic concentrations of insulin (10 micrograms/ml), EGF-induced cell proliferation could only be detected at a concentration of 50 ng/ml as opposed to a concentration of 2.0 ng/ml in the absence of insulin. This study suggests that insulin stimulates intestinal crypt cell proliferation only in supraphysiologic concentrations in a manner more characteristic of IGF-I than insulin, while producing enhanced binding of EGF to its receptor as well as an elevated threshold to EGF induced cell proliferation.

Cell Division↗

PubMed1989

Effects of timing of administration and dose of difluoromethylornithine on rat colonic carcinogenesis.

During azoxymethane (AOM)-induced colonic carcinogenesis in rats, biphasic induction of ornithine decarboxylase (ODC) activity occurs in the colonic mucosa. The relative contributions of these two phases of ODC induction to the carcinogenesis process were examined by studying the effects of the specific ODC inhibitor, difluoromethylornithine (DFMO), administered during either the initial phase of ODC increase or during both phases continuously. The effects of 1% and 0.25% DFMO administered continuously were also compared. Continuous oral administration of DFMO at 1% (approximately 8 mg/g body wt/wk) and 0.25% (approximately 2 mg/g body wt/wk) produced 93% inhibition of ODC induction by AOM in the right and left colons throughout the study. Despite suppression of ODC activity to near-normal levels, colon tumor incidence at 26 weeks in the right colon was not affected by either initial-phase or continuous administration of DFMO. In contrast, tumor incidence in the left colon was reduced from 35% to 5% by DFMO given continuously at doses of both 1% and 0.25% over the entire 26 weeks (P less than .05). No significant reduction in left colon tumor incidence resulted from the short initial 11-week course of DFMO although the tumor incidence was reduced (15% vs. 35%). Results suggest that the second ("post-initiation") phase of ODC induction may be of particular importance in carcinogenesis.

Animals↗

PubMed1989

Activity of batracylin (NSC-320846) against solid tumors of mice.

Batracylin (NSC 320846) is a water insoluble, solid tumor active compound discovered by the Development Therapeutics Program of the National Cancer Institute (NCI). In vivo, the NCI found this compound to be highly active [median treated tumor mass/median control tumor mass (T/C) = 0 to 20%] both orally and intraperitoneally against colon 38. In a disk diffusion, soft agar colony formation assay (500 ug/disk), we found solid tumor selectively (compared to leukemia L1210) against colon adenocarcinoma 38 (0-170 zu:L1210 leukemia; greater than 950 zu:C8), colon adenocarcinoma 9 (0-170 zu:L1210; greater than 950 zu:C9), colon adenocarcinoma 7/A (0-170 zu:L1210; 250-400 zu:C7), and pancreas ductal carcinoma 03 (0-170 zu:L1210; greater than 950 zu:Panc 03 (200 zone units [zu] = 6.5 mm zone of inhibition of cultured tumor colonies from drug disk). In vivo we have tested batracylin against mammary adenocarcinoma 16/C, colon 9, colon 38, colon 51, Panc 03, and hepatoma 129. Upon oral administration, batracylin was effective against colon 9 (T/C = 2.4%) and marginally active against colon 38 (T/C = 39%). Batracylin was orally ineffective against Panc 03 (T/C greater than 100%), colon #51 (T/C = 77%) and hepatoma 129 (T/C greater than 100%). Upon subcutaneous administration, batracylin was effective against colon #9 (T/C = 0%), and Panc 03 (T/C = 15%) but ineffective against mammary 16/C (T/C greater than 100%). At efficacious doses, delayed neurotoxicity, hepatic toxicity and a significant host weight loss was noted (with slow recovery). Both our in vitro data and the NCI in vivo data confirm its scant activity against L1210 (%ILS = 8 to 16%). Although showing activity against selected murine solid tumors, it lacked curative potential with early stage disease [C38, C9, Panc 03] and has shown relative inactivity in vitro against human solid tumor cell lines (H-125, CX-1, HCT-8, HCT-116). Batracylin has entered large animal toxicology trials at the NCI, anticipating phase I clinical evaluation.

Adenocarcinoma↗

PubMed1989

Efficacy of screening flexible sigmoidoscopy for colorectal neoplasia in asymptomatic subjects.

PURPOSE: Although flexible sigmoidoscopy is recommended in patients over age 40 to complement fecal occult blood screening for colorectal neoplasia, the yield of this procedure in asymptomatic, average-risk subjects has varied between studies. In addition, the efficacy of flexible sigmoidoscopy in detecting early curable carcinoma has been the subject of debate. We therefore undertook this study to assess the efficacy, safety, and cost of the procedure for early detection of colorectal neoplasia in asymptomatic subjects. PATIENTS AND METHODS: Flexible sigmoidoscopy with a 60-cm scope was performed in 412 asymptomatic veterans (mean age, 63.2 years). Subjects with positive fecal occult blood and those at increased risk for colorectal neoplasia were excluded. Costs were estimated on the basis of Medicare payments. RESULTS: A mean length of 56.1 cm of sigmoid and descending colon was examined. A total of 132 polyps were detected in 93 subjects (22.6%). Thirty-five percent of the polyps were located at a distance of greater than 30 cm from the anal verge. Of 122 polyps removed, 26% were 1 cm in size or larger. A total of 77 polyps (63%) were adenomas, and six polyps (5%) were carcinomas. Of the six carcinomas detected (two carcinoma in situ, one Astler Coller stage A, two stage B1, and one stage C1), five were in a localized stage and thus potentially curable. The cost of detecting each potentially curable carcinoma was $47,174. No complications from flexible sigmoidoscopy were noted. CONCLUSION: In conclusion, 60-cm flexible sigmoidoscopy is a safe, high-yield procedure for the initial screening of colorectal neoplasia in asymptomatic, average-risk subjects over the age of 50. Because the carcinomas detected were still in an early stage, such screening may improve survival.

Adenoma↗

PubMed1989

Prevention of colon cancer in primary care practice.

Colorectal cancer is a common disease with a high mortality rate. Surgical resection in early stages is the only effective treatment, therefore, recent attention is focused on diagnosing early colon cancer by screening asymptomatic subjects. Principles and current technology supporting early detection of colorectal cancer are critically evaluated. Current guidelines for screening average risk asymptomatic subjects and high-risk groups are discussed.

Colonic Neoplasms↗

PubMed1988

Alpha-difluoromethylornithine-induced inhibition of growth of autochthonous experimental colonic tumors produced by azoxymethane in male F344 rats.

Ornithine decarboxylase, the first regulatory enzyme in polyamine biosynthesis, is inhibited by alpha-difluoromethylornithine (DFMO), a specific enzyme-activated irreversible inhibitor. DFMO has been shown previously to inhibit experimental colonic tumorigenesis in rodents given the large bowel carcinogen azoxymethane or dimethylhydrazine. Therefore, we assessed the effects of DFMO on growth of established autochthonous experimental colonic tumors. Ten-wk-old male F344 rats were given 10 weekly s.c. injections of azoxymethane, 10 mg/kg. Starting 5 wk after the last dose, colonoscopy to the splenic flexure was performed weekly with a pediatric fiberoptic bronchoscope. When a tumor was visualized, its growth was assessed by computer image analysis of weekly colonoscopic photographs which included a scale. After two measurements for baseline tumor growth, the tumor-bearing rats were assigned in predetermined alternating sequence to the DFMO group (n = 26) or control group (n = 28). DFMO, 30 mg/ml (3%), was given in drinking water for 4 wk, resulting in mean weekly intake of 16 +/- 1 (SE) to 18 +/- 1 mg of DFMO/g of body weight. Control rats were pair-fed, resulting in reduced body weights comparable to DFMO rats. DFMO dramatically inhibited tumor growth, beginning in the first week of administration: mean tumor volume of DFMO rats reached only 7.0 +/- 2.0 mm3 compared with 17.4 +/- 3.2 mm3 in controls (P less than 0.02); and tumors in three DFMO rats disappeared. Mean change in tumor volume in DFMO rats was less than controls during all 4 wk of administration, although there was a suggestion of escape from DFMO suppression of tumor growth in the last 2 wk. At necropsy, tumor ornithine decarboxylase activity was 115 +/- 22 pmol/h/mg of protein in DFMO rats as compared with 842 +/- 576 in controls. There was a suggestion of greater tumor desmoplasia in DFMO rats, but tumor differentiation, depth of invasion, inflammation, and labeling index with tritiated thymidine showed no statistically significant differences between the DFMO and control groups. Our findings suggest that (a) ornithine decarboxylase plays a key role in growth of autochthonous experimental colonic tumors, and (b) DFMO may have potential for chemotherapy and chemoprophylaxis of colorectal neoplasms in human beings.

Animals↗

PubMed1988

The growth-inhibitory effect of 4-hydroperoxycyclophosphamide against human non-small cell lung carcinoma is enhanced by low-dose difluoromethylornithine.

Surgically unresectable human non-small cell lung carcinoma (NSCC) is highly resistant to present chemotherapy and radiation therapy regimens. Cyclophosphamide, a potent alkylating agent, has shown some efficacy, especially in combination chemotherapy. Difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase (ODC) which produces minimal toxicity in animals and humans, has shown antiproliferative effect against human SCC in culture but a much smaller effect (cytostatic) against NSCC. We therefore investigated 4-hydroperoxycyclophosphamide (4HC) and DFMO alone and in combination against a human NSCC line (NCI-H157). Cells were treated with DFMO at graded concentrations of 0 to 800 microM from day 0 to day 7. On day 3, cells were exposed for 1 h to 4HC at graded concentrations of 0 to 80 microM, washed, and refed with media containing DFMO at initial concentrations. On day 7, cells were counted by hemacytometer. Cells treated with DFMO or 4HC alone exhibited dose-dependent growth inhibition. Growth inhibition by 4HC was enhanced through combination with DFMO. On day 7, 50 microM (5 x 10(-5) M) DFMO effected a 37% inhibition, 8 microM 4HC 47% inhibition, and the combination of 50 microM DFMO and 8 microM 4HC yielded an elevated 71% inhibition. The growth inhibitory effect and potentiating effect of DFMO were reversible upon addition of putrescine (PU) to the culture medium. The combination of DFMO and 4HC, two agents with different toxicity spectra, may represent an effective chemotherapeutic regimen for the treatment of lung cancer.

Carcinoma, Non-Small-Cell Lung↗

PubMed1988

Distribution of polyamines and their biosynthetic enzymes in intestinal adaptation.

Ornithine decarboxylase (ODC) and the polyamines have been shown to be important for growth processes in the intestinal mucosa. The highest activity of ODC is found in the differentiated, nonproliferating villus-tip cells rather than in the rapidly proliferating undifferentiated crypt cells. During poststarvation refeeding and lactation, we now show that increases in ODC activity paralleled the time course of mucosal hyperplasia and thymidine incorporation. Increases in ODC (threefold) were similar in villus and crypt cells, and the villus-crypt gradient of decreasing ODC activity (40:1) was maintained. The activity of the other polyamine biosynthetic enzyme, S-adenosylmethionine decarboxylase (SDC), was highest in the crypt cells in the basal state and increased throughout the entire villus-crypt axis during refeeding and lactation, preserving a villus-crypt gradient opposite to that of ODC. During hyperplasia, all three polyamines increased. Putrescine was highest in the villus-tip cells, paralleling ODC activity, whereas spermidine and spermine were highest in the crypt cells and paralleled the distribution of SDC activity. Thus SDC activity and spermidine and spermine content may play a more important role than ODC and putrescine in regulation of intestinal mucosal proliferation. It is also possible that the threefold increases in the low levels of ODC in the crypt cells are adequate to trigger cell proliferation, whereas the higher ODC levels in villus cells may represent an association with the differentiation of the enterocytes.

Adaptation, Physiological↗

PubMed1988

Ornithine decarboxylase as a marker for colorectal polyps and cancer.

There is as yet no specific chromosomal abnormality or gene marker identified for colorectal polyps and cancer. Thus available markers include only phenotypic markers. Tumor markers that have been studied include tetraploidy and increased colonic mucosal proliferation; and these markers have identified those patients that are at high risk for colon cancer. The current "gold standard" of colorectal cancer markers is the carcinoembryonic antigen (CEA). CEA is best used as a monitor of disease and recurrence, and not as a screening or diagnostic test. Newer carbohydrate markers include CA 19-9, incompatible A and B antigens, and T and Lewis antigens. These markers have not shown increased specificity or sensitivity compared to CEA. An interesting recently described marker is ornithine decarboxylase (ODC), which serves as a simple overall index of colonic mucosal proliferation. Ornithine decarboxylase levels have shown correlation with the progression from normal mucosa to adenoma and carcinoma, especially in hereditary polyposis syndromes. This enzyme may also serve as a potential therapeutic target. Many markers have been found useless in further clinical trials. Ornithine decarboxylase needs to be studied in greater detail to determine its sensitivity and specificity, in patients with hereditary colonic neoplasia and in patients without genetic syndromes.

Biomarkers, Tumor↗

PubMed1988

Clinical features, evaluation, and detection of colorectal cancer.

The most common presentation of colorectal carcinoma is in the symptomatic patient, most often with complaints of rectal bleeding, abdominal pain, or change in bowel habits. Symptomatic patients often have advanced disease and, because surgical resection is the only effective therapy at present, their chance for cure is poor. Until effective treatment is available, therefore, we must identify patients at high risk for lifelong screening. In addition, more effective means of surveillance of the general population need to be developed in order to diagnose patients at risk for sporadic colorectal cancer, given that this represents the majority of patients with disease. Tumor markers also would be useful to find residual disease while it is still resectable in patients who have undergone surgery for curative resection.

Colorectal Neoplasms↗

PubMed1988

Life after colectomy.

Animal and epidemiologic studies have raised hopes that effective chemoprevention of colorectal cancer in very high-risk patients may be possible in the future, but at present, the only established effective way to prevent colorectal cancer in very high-risk patients is colectomy. Advances in surgical techniques, improvements in stomal appliances, and medical advances in dealing with complications of colorectal surgery (such as impotence) have contributed to substantial improvements in the quality of life of patients who have had prophylactic colectomies.

Colectomy↗