In vivo kinetics of oleic, linoleic, and α-linolenic acid biohydrogenation in the rumen of dairy cows

Ruminal biohydrogenation (BH) of unsaturated fatty acids (FA) reduces absorption of essential FA and can result in formation of bioactive FA that cause milk fat depression. Rates of biohydrogenation of unsaturated FA are commonly observed using in vitro systems and are not well described in vivo. Seven ruminally cannulated cows were enrolled in a 3 × 3 Latin square design study to quantify biohydrogenation of 18:1n-9, 18:2n-6, and 18:3n-3 using a recently developed in vivo BH assay. All cows were fed a common high corn silage basal diet. Biohydrogenation was quantified using a perturbation model that consisted of a bolus dose of 200 g of an oil enriched in each unsaturated FA (oleic acid, OA = 87% 18:1n-9 sunflower oil; linoleic acid, LA = 70% 18:2n-6 safflower oil; and α-linolenic acid, ALA = 54% 18:3n-3 flaxseed oil) and 12 g of 17:0 as a marker of rumen outflow. Rumen contents were sampled before and after the bolus and enrichment of the bolused FA modeled. Using first-order kinetics to model FA disappearance, the fractional rates of disappearance of 18:1n-9 was 0.597 per hour, 18:2n-6 was 0.618 per hour, and 18:3n-3 was 0.834 per hour, similar to rates previously reported with this approach. Rumen turnover of 17:0 was 0.123 per hour, 0.065 per hour, and 0.106 per hour during the OA, LA, and ALA treatments, respectively. The extents of BH were calculated to be 82.8, 90.4, and 88.6% for 18:1n-9, 18:2n-6, and 18:3n-3, respectively. Finally, compartmental modeling was used to quantify the amount of each unsaturated FA metabolized through trans-10 and trans-11 BH pathways. The recently developed in vivo BH assay was able to predict rates of BH and provide insight into rumen metabolism of individual FA and may be useful to future investigations.

Association between serum retinol-binding protein 4 concentrations and clinical indices in subjects with type 2 diabetes: a meta-analysis

BACKGROUND

Retinol-binding protein (RBP4) is an adipokine that may be important in type 2 diabetes. Previous studies have examined the association between serum RBP4 concentrations and clinical indices in patients with type 2 diabetes, although the results obtained have been inconsistent. We conducted a meta-analysis aiming to investigate the association between serum RBP4 concentrations and clinical indicators of diabetes, renal function, metabolic syndrome and obesity in subjects with type 2 diabetes.

METHODS

MEDLINE, EMBASE and CINAHL databases were searched from 2005 through November 2011, and the search identified 21 clinical variables from seven studies (total n = 1406). For each variable, summary correlation coefficients (r(s) ) were estimated using a random-effects meta-analysis.

RESULTS

None of the diabetes markers were correlated with serum RBP4 concentrations in subjects with type 2 diabetes, whereas all of the renal function markers and many metabolic syndrome markers were significantly correlated. Summary correlation coefficients and 95% confidence intervals (CIs) were -0.36 (95% CI = -0.51 to -0.18) for creatinine clearance, -0.39 (95% CI = -0.44 to -0.33) for estimated glomerular filtration rate and 0.53 (95% CI = 0.30-0.71) for creatinine concentration. In addition, plasma triglyceride concentrations (r(s) = 0.22; 95% CI = 0.11-0.32), plasma total cholesterol concentrations [r(s) = 0.14 (95% CI = 0.05-0.23)] and low-density lipoprotein cholesterol level (r(s) = 0.14; 95% CI = 0.02-0.25) were positively correlated with serum RBP4 concentrations.

CONCLUSIONS

The results obtained in the present study suggest that serum RBP4 concentrations in patients with type 2 diabetes may be associated with diabetes-related renal dysfunction and imbalances in lipid metabolism.

Hyaluronan: a potential carrier for growth factors for the healing of ligamentous tissues

The anterior cruciate ligament has little capacity to heal after injury, in contrast to the medial collateral ligament. Cell migration and cell proliferation are essential steps in the wound healing of connective tissue, and we have developed an in vitro assay to study cell outgrowth (i.e., both cell migration and cell proliferation) from tissue explants. Using this assay, we have previously shown a synergistic effect of four growth factors on the early stages of cell outgrowth (i.e., at days 3 and 6) from these explants. Hyaluronan, a linear polysaccharide with a molecular weight of 3 x 10(6) daltons, has been shown to enhance the anterior cruciate ligament healing capacity in vivo by over 50%. The purpose of this study was to assess in vitro whether hyaluronan and the combination of growth factors (transforming growth factor-beta1 25 ng/ml, platelet-derived growth factor-BB 100 ng/ml, basic fibroblast growth factor 100 ng/ml, and insulin 25 microg/ml) would enhance cell outgrowth from explants at 3 and 6 days. At 3 days the mean cell outgrowth from the explants treated with hyaluronan and the combination of growth factors exceeded the growth in the explants treated with growth factors alone for the anterior cruciate ligament (mean cell count +/- standard error: 19 +/- 4 and 2 +/- 1 cells, respectively) and for the medial collateral ligament (297 +/- 40 and 87 +/- 18 cells, respectively). At 6 days, the mean cell outgrowth in the presence of growth factors was enhanced sixfold by hyaluronan for the anterior cruciate ligament (160 +/- 27 compared with 26 +/- 15 cells) and fourfold for the medial collateral ligament (1363 +/- 219 compared with 330 +/- 74 cells). As previously shown, little cell outgrowth occurred from the anterior cruciate or medial collateral ligament explants when no growth factors were added to the modified Eagle's media at 3 and 6 days (<20 cells). For the medial collateral ligament only, hyaluronan had a small stimulatory effect on cell outgrowth in minimal essential media in the absence of growth factors. At 3 days the stimulation by hyaluronan was fourfold (31 +/- 8 cells compared with 7 +/- 4 cells), and at 6 days the stimulation by hyaluronan was nearly fourfold (73 +/- 17 compared with 20 +/- 12 cells). These results suggest that hyaluronan could be used together with growth factors in efforts to enhance the healing of ligamentous tissue injuries.

Vitamin A intake and status influence retinol balance, utilization and dynamics in rats

To study effects of vitamin A status on retinol dynamics, male rats were fed purified diets varying in vitamin A concentration. Group 1 rats had marginal liver vitamin A levels (approximately 500 nmol) and were in a slight positive vitamin A balance; Group 2 had similar liver levels but were in a slight negative balance; Group 3 had lower liver levels (approximately 370 nmol) and were in a slight negative balance; Group 4 had depleted liver reserves (<10 nmol) and were in vitamin A balance. [3H]Retinol-labeled plasma was injected intravenously, and serial plasma samples were collected for 41 d while rats (six per group) consumed approximately 50 nmol retinol/d (Group 1) or -25 nmol/d (Groups 2-4). Plasma retinol was normal in Groups 1-3 (1.9-2.0 micromol/L) and lower in Group 4 (0.96 micromol/L). Plasma tracer data were fit to a three-compartment model. The central plasma retinol compartment (transit time, 1.5-1.7 h) exchanged with a fast turning-over extravascular vitamin A pool (transit time, 3-4.5 h; -40 nmol) and with a larger, slow turning-over extravascular pool (transit time, 5.5-10 d) that was the site of irreversible utilization of vitamin A. Irreversible utilization was 36 nmol/d (Group 1), 29 nmol/d (Groups 2 and 3) and 20 nmol/d (Group 4). The data indicate that in rats with low or marginal vitamin A status, vitamin A intake, vitamin A reserves and plasma retinol concentration all influence vitamin A utilization and other aspects of retinol dynamics.

Lactoferrin interaction with retinoid signaling: cell growth and apoptosis in mammary cells

Lactoferrin (Lf) is a multifunctional iron-binding protein that was first identified in mammary secretions, but is synthesized by most mammalian tissues. The protein has a signal sequence that dictates secretion; it also has a nuclear localization sequence that facilitates entry into the cell nucleus. The mechanism of the latter action is currently unknown, but is thought to occur via a Lf receptor. Lactoferrin content of mammary tissue and secretions varies with developmental state; it is synthesized in mammary tissue at high levels during both pregnancy and involution, and during mammary infections. Using fluorescent (FITC)-labeled holo-bLf, we show that bovine primary epithelial cells and MCF-7 breast cancer cells do not translocate the exogenously added Lf to the nucleus after culture in serum free media (SFM). However, the supplementation of SFM with 1microM all-trans retinoic acid (atRA) caused breast cancer cells to gain the capacity to take up labeled bLf into the cell nucleus. Primary bovine mammary cells (MeBo) exhibited similar capacity in culture. This suggests that in addition to Lf, one or more components modulated by atRA, are necessary for nuclear translocation to occur. Transfection experiments with atRA treated MCF-7 cells containing retinoic acid response element reporter constructs showed that the extracellular application of lactoferrin alters reporter gene expression. Lactoferrin increased a DR5 luciferase response element in a dose-dependent manner only when atRA was applied. Immunocytochemical markers for the cell cycle (Ki67) and apoptotic events (Caspase-3 and PARP-85) showed that lactoferrin alters the atRA-induced phenotype, blocking apoptosis and maintaining cell cycle activity in both MCF-7 and MeBo cells in the presence of 1muM atRA. We propose that nuclear lactoferrin interacts with retinoic acid signaling pathways in cells and alters/blocks the signals so that cells remain in the cell cycle and/or do not enter the apoptotic pathway.

Oxidative DNA damage induced by high glucose and its suppression in human umbilical vein endothelial cells

In order to investigate the mechanism of the production of oxidative DNA damage by hyperglycemia, we measured formamidopyrimidine N-glycosylase (FPG)-sensitive sites by the comet assay in human umbilical vein endothelial cells (HUVECs) cultured under various conditions including high glucose. Mean values of FPG-sensitive sites were higher in HUVECs cultured for 5 days in high glucose (45 mM) compared with normal glucose (5mM) medium (P<0.001). FPG-sensitive sites increased in a time-dependent manner under high glucose treatment (3 days: P<0.05, 5 days: P<0.001), whereas L-glucose, which is taken up poorly into the cells, gave a slight increase in FPG-sensitive sites (P<0.05). Flow cytometric analysis using 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate, di(acetoxymethyl ester) showed that incubation with L-glucose produced more reactive oxygen species than incubation with D-glucose. However, these increases were slight (1.22- and 1.12-folds, respectively). Incubation of HUVECs with aminoguanidine (100 microM) or pyridoxamine (1mM), which are inhibitors of glycation, decreased the levels of FPG-sensitive sites (P<0.001). However, these inhibitors did not suppress the intracellular generation of reactive oxygen species induced by high glucose. These results indicate that FPG-sensitive sites induced by high glucose are not due to intracellular reactive oxygen species. In order to clarify what caused the induction of FPG-sensitive sites, we investigated the effect of glyoxal and 3-deoxyglucosone (3-DG) on the induction of FPG-sensitive sites and the intracellular production of reactive oxygen species in HUVECs. Glyoxal and 3-DG at a concentration of 100 microg/ml induced FPG-sensitive sites (P<0.001, P<0.01, respectively). In contrast, glyoxal did not generate reactive oxygen species inside HUVECs. The results shown in this study suggest that glyoxal formed intracellularly or extracellularly during high glucose treatment might induce FPG-sensitive sites by a mechanism not involving reactive oxygen species.

Haemobilia

BACKGROUND

This review aims to establish whether increased use of invasive procedures and the trend toward conservative management of major trauma has resulted in an increased incidence of haemobilia.

METHOD

A Medline (http://igm.nlm.nih.gov/)-based search of the English language literature from January 1996 to December 1999 inclusive was performed using the keywords haemobilia, hemobilia, haematobilia and hematobilia. The presentation, aetiology, investigation, management and outcome of 222 cases were reviewed.

RESULTS

Two-thirds of cases were iatrogenic while accidental trauma accounted for 5 per cent. Haemobilia may be major, constituting life-threatening haemorrhage, or minor; it may present many weeks after the initial injury. Diagnosis is most commonly confirmed by angiography. Management is aimed at stopping bleeding and relieving biliary obstruction; 43 per cent of cases were managed conservatively and 36 per cent were managed by transarterial embolization (TAE). Surgery was indicated when laparotomy was performed for other reasons and for failed TAE. The mortality rate was 5 per cent.

CONCLUSIONS

Although the incidence of iatrogenic haemobilia has risen considerably, the bleeding is often minor and can be managed conservatively. When more urgent intervention is required, TAE is usually the treatment of choice. There is no evidence that the conservative management of accidental liver trauma increases the risk of haemobilia.

Contrasting effects of an ultraviolet B and an ultraviolet A tanning lamp on interleukin-6, tumour necrosis factor-alpha and intercellular adhesion molecule-1 expression

BACKGROUND

Recent studies have demonstrated that a tanning lamp emitting predominantly ultraviolet (UV) A induces significant yields of the type of potentially mutagenic DNA damage that are associated with the onset of skin cancer (i.e. cyclobutane pyrimidine dimers). UV-induced immunosuppression is also an important event leading to skin cancer.

OBJECTIVES

To the modulation of key immunological molecules following exposure to a broad-spectrum UVB lamp and a predominantly UVA-emitting tanning lamp using model in vitro systems.

METHODS

We compared secretion and mRNA expression of interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha in normal human epidermal keratinocytes, and interferon (IFN)-gamma-induced intracellular adhesion molecule (ICAM)-1 in normal human fibroblasts irradiated in vitro with a broad-spectrum UVB lamp or with a Philips 'Performance' tanning lamp.

RESULTS

With broad-spectrum UVB irradiation, upregulation of IL-6 and TNF-alpha mRNA was detected 6 h after irradiation, and a dose-dependent increase of cytokines in the supernatants of irradiated cells was found 24 h after irradiation. In contrast, there was no cytokine secretion and little evidence for mRNA upregulation following exposure to a tanning lamp. When cells were exposed first to broad-spectrum UVB, then the tanning lamp, UVB-induced cytokine secretion was inhibited, although mRNA levels were upregulated to a level close to that observed with UVB alone. By using a Schott WG 320 nm filter to attenuate the level of UVB relative to UVA emitted by the tanning lamp, the inhibition of cytokine secretion was shown to be associated with UVA exposure. Both UV sources inhibited IFN-gamma-induced ICAM-1 mRNA expression in a dose-dependent fashion. By using a Schott WG 335 nm filter, inhibition of ICAM-1 mRNA expression by the tanning lamp was shown to be associated with UVB exposure.

CONCLUSIONS

These results suggest that UV sources emitting different levels of UVA and UVB have differential effects on the modulation of different immunoregulatory molecules, and indicate that there are potential interactions between these wavelengths.

Haemobilia

BACKGROUND

This review aims to establish whether increased use of invasive procedures and the trend toward conservative management of major trauma has resulted in an increased incidence of haemobilia.

METHOD

A Medline (http://igm.nlm.nih.gov/)-based search of the English language literature from January 1996 to December 1999 inclusive was performed using the keywords haemobilia, hemobilia, haematobilia and hematobilia. The presentation, aetiology, investigation, management and outcome of 222 cases were reviewed.

RESULTS

Two-thirds of cases were iatrogenic while accidental trauma accounted for 5 per cent. Haemobilia may be major, constituting life-threatening haemorrhage, or minor; it may present many weeks after the initial injury. Diagnosis is most commonly confirmed by angiography. Management is aimed at stopping bleeding and relieving biliary obstruction; 43 per cent of cases were managed conservatively and 36 per cent were managed by transarterial embolization (TAE). Surgery was indicated when laparotomy was performed for other reasons and for failed TAE. The mortality rate was 5 per cent.

CONCLUSIONS

Although the incidence of iatrogenic haemobilia has risen considerably, the bleeding is often minor and can be managed conservatively. When more urgent intervention is required, TAE is usually the treatment of choice. There is no evidence that the conservative management of accidental liver trauma increases the risk of haemobilia.

Increased rat mammary tissue vitamin A associated with increased vitamin A intake during lactation is maintained after lactation

Although increases in dietary vitamin A increase milk vitamin A, little is known about effects of vitamin A intake on mammary tissue vitamin A levels during and after the reproductive cycle. First, we measured vitamin A concentrations in milk, mammary tissue and liver of lactating rats fed 0, 4, or 50 micromol of vitamin A/kg diet during pregnancy and through d 12 of lactation. Liver vitamin A concentration was significantly affected by diet in lactating females and pups 12 d after parturition. Milk vitamin A concentrations were significantly higher (7.1 +/- 2.2 micromol/L, n = 8) in dams fed 50 micromol/kg than in those fed 0 or 4 micromol/kg (1.9 +/- 0.3, n = 5 and 2.9 +/- 0.7 micromol/L, n = 7; P < 0.001), as were mammary tissue vitamin A concentrations (5.1 +/- 1.1 versus 2.2 +/- 0.4 and 2.4 +/- 0.6 nmol/g; P < 0.001). Next, we maintained female rats on 50 or 10 micromol vitamin A/kg diet during pregnancy and lactation and then on 4 micromol/kg diet after pups were weaned on d 21. On d 21, mammary tissue vitamin A concentrations were 3.14 +/- 0.75 versus 1.52 +/- 0.21 nmol/g in dams fed 50 versus 10 micromol/kg (n = 4/group; P < 0.001). Mammary tissue vitamin A concentrations were not significantly affected by time from 7 to 49 d after lactation and averaged 8.5 +/- 0.4 and 4.9 +/- 0.8 nmol/g on d 49 in dams fed 50 versus 10 micromol/kg (n = 4; P < 0.001). We conclude that diet-induced differences in rat mammary tissue vitamin A developed during pregnancy and lactation are maintained for > or =7 wk after lactation.

Vitamin A intake affects the contribution of chylomicrons vs. retinol-binding protein to milk vitamin A in lactating rats

To investigate the influence of vitamin A intake on the contribution of chylomicrons vs. holo retinol-binding protein to milk vitamin A, female rats were fed diets containing either 10 (n = 6) or 50 micromol vitamin A/kg body (n = 4) during pregnancy and through d 13 of lactation. [3H]Vitamin A was incorporated into each diet beginning on d 6 of lactation. Vitamin A concentrations on d 13 were significantly higher in dam liver (x 3), pup liver (x 2.6), milk (x 2.5) and mammary tissue (x 1.3) in rats consuming the higher level of vitamin A. In both groups, vitamin A specific activities in plasma and milk reached apparent plateaus by 2.33 d after addition of [3H]vitamin A to the diets. Vitamin A specific activity in milk was higher than in plasma at all times in both groups. The estimated minimum contribution of chylomicrons to milk vitamin A was 32 +/- 3% in rats fed the lower level of vitamin A vs. 52 +/- 10% at the higher level (P = 0.014). We concluded that dietary vitamin A, like triglycerides, may be directed to mammary tissue during lactation for preferential secretion into milk; thus, increasing vitamin A intakes will increase the contribution of dietary vitamin A to milk. In contrast to milk, mammary tissue vitamin A turns over very slowly.

CD40 ligation for immunotherapy of solid tumours

Tumour vaccines provide an important focus of current cancer research and are often based on the premise that although T-cells do respond naturally to certain tumours, this is usually weak and therefore ineffective at controlling disease. An integral and necessary part of a T-cell immune response involves triggering of CD40 on antigen-presenting cells (APC) by its ligand, CD154, on responding T helper (Th) cells. Furthermore, cytotoxic responses to tumours may fail because the Th-cell response is inadequate and unable to provide CD40 stimulation of APC. Growing evidence shows that stimulating APC with soluble CD40L or an agonistic anti-CD40 mAb can, at least in part, replace the need for Th cells and generate APC that are capable of priming cytotoxic T lymphocytes (CTL). The aim of this study was to investigate whether a range of solid tumours (CD40(-)) could be treated with anti-CD40 mAb. It was found that this treatment was effective, and correlated with the intrinsic immunogenicity and aggressiveness of the tumours. The mAb could be delivered locally or at a distal site, but increased antigen load provided by irradiated tumour cells added little to the effectiveness of the treatment. T-cells were required since cytokine (interferon-gamma) and CTL activity were demonstrated following treatment and the therapeutic efficacy was lost in nude mice. In addition, depletion of CD8(+) cells abrogated protection whilst depletion of CD4(+) cells had no effect. This study demonstrates that solid CD40(-) tumours are sensitive to anti-CD40 mAb therapy and that the response bypasses the need for Th cells.

Ultraviolet-B-induced apoptosis and cytokine release in xeroderma pigmentosum keratinocytes

We have assessed the ability of xeroderma pigmentosum and normal keratinocytes grown out from skin biopsies to undergo apoptosis after irradiation with ultraviolet B. Keratinocytes have been studied from xeroderma pigmentosum complementation groups A (three biopsies), C (three biopsies), D (one biopsy), xeroderma pigmentosum variant (two biopsies), and Cockayne syndrome (one biopsy). The three xeroderma pigmentosum group A and the xeroderma pigmentosum group D samples were at least six times more sensitive than normal cells to ultraviolet B-induced apoptosis. The xeroderma pigmentosum variant samples showed intermediate susceptibility. Xeroderma pigmentosum group C samples proved heterogeneous: one showed high sensitivity to apoptosis, whereas two showed near normal susceptibility. The Cockayne syndrome sample showed the high susceptibility of xeroderma pigmentosum groups A and D only at a higher fluence. These results suggest that the relationships between repair deficiency, apoptosis, and susceptibility to skin cancer are not straightforward. Ultraviolet B-induced skin cancer is also thought to be due in part to ultraviolet B-induced impairment of immune responses. The release of the inflammatory cytokines interleukin-6 and tumor necrosis factor-alpha from cultured xeroderma pigmentosum keratinocytes tended to occur at lower fluences than in normals, but was less extensive, and was more readily inhibited at higher fluences of ultraviolet B.

Immunomagnetic purification of beta cells from rat islets of Langerhans

AIMS/HYPOTHESIS

The aim of this study was to develop immunomagnetic purification by the Dynabead system to separate insulin-containing beta cells from a mixed rat islet cell population. Functional studies on insulin secretion and a test of the susceptibility of Dynabead-separated beta cells to DNA damage following cytokine exposure were carried out.

METHODS

Dynabeads are uniform, paramagnetic particles coated with specific antibodies. Single rat islet cells were initially incubated with the beta-cell surface specific antibody (K14D10 mouse IgG) for 20-60 min. A suspension of Dynabeads coated with a secondary antibody (anti-mouse IgG) was added for a further 15 min, after which the Dynabead-coated cells were instantaneously pelleted by contact between the tube and a magnet (Dynal MPC). Immunocytochemistry was used to confirm that the Dynabead-coated cells contained insulin and to quantify the efficiency of the method. Dynabead-coated and non-coated cells were stained for insulin and glucagon.

RESULTS

Dynabead immunopurification yielded 95% pure insulin-containing beta cells, which released insulin in response to isobutylmethylxanthine and glucagon-like polypeptide 1. The insulin content of Dynabead-coated beta cells was significantly higher than that of non-coated cells. Successful separation was achieved using as few as 30 islets as starting material. Using the comet assay, we found that Dynabead-coated beta cells showed equal susceptibility to cytokine-induced DNA damage as non-coated cells.

CONCLUSION/INTERPRETATION

We conclude that Dynabead separation of beta cells is simple, rapid, applicable to large or small numbers of islets and can be used to study beta-cell specific function and responsiveness.

Apoptosis and cytokine release induced by ionizing or ultraviolet B radiation in primary and immortalized human keratinocytes

We have compared the induction of apoptosis and cytokine release by UVB and gamma-radiation in primary (untransformed) and in two immortalized human epithelial/keratinocyte cell lines, HaCaT and KB (KB is now known to be a subline of the ubiquitous keratin-forming tumour cell line HeLa and we therefore designate it HeLa-KB). In both the primary and the immortalized cell lines apoptosis and release of the inflammatory cytokine interleukin-6 are induced rapidly following UVB irradiation. In contrast, only the immortalized cells undergo apoptosis and release interleukin-6 after gamma-irradiation and here the onset of apoptosis and cytokine release are delayed. The same distinction between primary and immortalized cells was observed when double-strand breaks were induced with the anticancer drug mitoxantrone, which stabilizes topoisomerase II-cleavable complexes. We suggest that immortalization may sensitize keratinocytes to the apoptogenic effect of ionizing radiation or mitoxantrone by deregulating normal cell cycle checkpoints. In both human keratinocytes and fibroblasts, cell killing, as assayed by loss of colony-forming ability, is not coupled to apoptosis. Immortalization increases resistance to gamma-radiation killing but sensitizes to apoptosis. In contrast, although immortalization also sensitizes to UVB-induced apoptosis, it does not affect UVB-induced cell killing. Apoptosis unambiguously indicates death at the single cell level but clonal cell survival integrates all the cellular and genetic processes which prevent or permit a scorable clone to develop.

Mobilization of vitamin A stores in rats after administration of 2,3, 7,8-tetrachlorodibenzo-p-dioxin: a kinetic analysis

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic environmental contaminant that prevents the normal accumulation of vitamin A in liver and causes increased excretion of vitamin A. To determine what alterations in vitamin A metabolism occur first in response to TCDD treatment, we administered TCDD (7.0 microg/kg b.w. ) orally to rats that had received a nonperturbing (tracer) iv dose of [(3)H]vitamin A-labeled plasma (n = 3) or lymph (n = 3) 21 days earlier. Within a few days after TCDD administration, fraction of the injected radiolabel in plasma, which had been in a terminal slope when plotted on a semilog scale, increased and remained elevated until the experiment was terminated (day 42). At that time, liver vitamin A levels were 65% lower in TCDD-perturbed rats than in controls. Using model-based compartmental analysis and compartmental models developed previously for control rats (S. K. Kelley et al., 1998, Toxicol. Sci, 44:1-13), we determined the minimal changes needed to account for the perturbation in plasma [(3)H] tracer responses after TCDD administration. We determined that the effects of TCDD could be explained by adjusting the value of one fractional transfer coefficient corresponding to the mobilization of vitamin A from large, slowly turning-over pools. We speculate that this change corresponds to an increased fractional rate of retinyl ester hydrolysis, and that it precedes the TCDD-associated increased irreversible utilization and excretion of vitamin A.

Kinetic analysis shows that iron deficiency decreases liver vitamin A mobilization in rats

In view of evidence that nutritional status of iron and vitamin A may affect the other nutrient's metabolism, we used model-based compartmental analysis to examine effects of iron deficiency on whole-body vitamin A dynamics in rats. Weanling male Sprague-Dawley rats were fed the AIN93G diet with 2.5 nmol retinyl palmitate/g and either 45 [control (CN)] or 4 microg/g Fe [iron-deficient (ID)] for 8 wk. ID rats consumed food ad libitum; CN rats were food-restricted so that their body weights were the same as ID rats. Two rats/group were killed; liver vitamin A was determined and used for vitamin A balance calculations. [(3)H]Retinol-labeled plasma was administered intravenously to remaining rats, and 27 serial blood samples were collected for 7 wk. At killing, plasma vitamin A was 0.52+/-0.12 (ID, n = 5) vs. 1.34+/-0.12 micromol/L (CN, n = 6; P<0.001), and liver vitamin A was 809+/-94 (ID) vs. 112+/-24 nmol (CN, P<0.001). Plasma tracer data were fit to a three- or four-compartment model using the Simulation, Analysis and Modeling computer program and kinetic parameters were calculated. Vitamin A transfer rate between the retinyl ester storage pool [14+/-3 (ID) vs. 24+/-4 nmol/d (CN), P<0.05] and plasma was lower in ID rats. Vitamin A remained longer in the body [44+/-11 (ID) vs. 22+/-3 d (CN), P<0.05]. Adjusted mean disposal rate was lower in ID (10.0) than CN rats (19.9 nmol/d), as was estimated vitamin A absorption efficiency [58% (ID) vs. 76% (CN)]. Our results suggest that iron deficiency inhibits mobilization of vitamin A stores and may decrease the absorption and irreversible utilization of vitamin A.

UV damage causes uncontrolled DNA breakage in cells from patients with combined features of XP-D and Cockayne syndrome

Nucleotide excision repair (NER) removes damage from DNA in a tightly regulated multiprotein process. Defects in NER result in three different human disorders, xeroderma pigmentosum (XP), trichothiodystrophy (TTD) and Cockayne syndrome (CS). Two cases with the combined features of XP and CS have been assigned to the XP-D complementation group. Despite their extreme UV sensitivity, these cells appeared to incise their DNA as efficiently as normal cells in response to UV damage. These incisions were, however, uncoupled from the rest of the repair process. Using cell-free extracts, we were unable to detect any incision activity in the neighbourhood of the damage. When irradiated plasmids were introduced into unirradiated XP-D/CS cells, the ectopically introduced damage triggered the induction of breaks in the undamaged genomic DNA. XP-D/CS cells thus have a unique response to sensing UV damage, which results in the introduction of breaks into the DNA at sites distant from the damage. We propose that it is these spurious breaks that are responsible for the extreme UV sensitivity of these cells.

The cancer-free phenotype in trichothiodystrophy is unrelated to its repair defect

The DNA repair-deficient genetic disorders xeroderma pigmentosum (XP) and trichothiodystrophy (TTD) can both result from mutations in the XPD gene, the sites of the mutations differing between the two disorders. The hallmarks of XP are multiple pigmentation changes in the skin and a greatly elevated frequency of skin cancers, characteristics that are not seen in TTD. XP-D and most TTD patients have reduced levels of DNA repair, but some recent reports have suggested that the repair deficiencies in TTD cells are milder than in XP-D cells. We reported recently that inhibition of intracellular adhesion molecule-1 (ICAM-1) expression by UVB irradiation was similar in normal and TTD cells but increased in XP-D cells, suggesting a correlation between ICAM-1 inhibition and cancer proneness. In the first part of the current work, we have extended these studies and found several other examples, including XP-G and Cockayne syndrome cells, in which increased ICAM-1 inhibition correlated with cancer proneness. However, we also discovered that a subset of TTD cells, in which arg112 in the NH2-terminal region of the XPD protein is mutated to histidine, had an ICAM-1 response similar to that of XP-D cells. In the second part of the work, we have shown that TTD cells with this specific NH2-terminal mutation are more sensitive to UV irradiation than other TTDs, most of which are mutated in the COOH-terminal region, and are indistinguishable from XP-D cells in cell killing, incision breaks, and repair of cyclobutane pyrimidine dimers. Because the clinical phenotypes of these patients do not obviously differ from those of TTDs with mutations at other sites, we conclude that the lack of skin abnormalities in TTD is independent of the defective cellular responses to UV. It is likely to result from a transcriptional defect, which prevents the skin abnormalities from being expressed.

Books as a source of medical education for women in the Middle Ages

The development of philosophical medicine in the high and late Middle Ages brought with it a powerful association of medical knowledge with the written word. To possess books, or at least to have access to books, was both a prerequisite for and a symbol of the kind of theoretical learning that distinguished the learned practitioner from the empiric. This study examines evidence for women's access to medical books, raising the question of what difference gender made. I argue that, for the most part, women did not own medical books, whether they were laywomen or religious. I suggest that this was largely due to the limits on advanced education for women, a factor that would have effected both laywomen and nuns.

Possible effects of sunlight on human lymphocytes

The human population is exposed to both the ultraviolet A (UVA) and B (UVB) regions of the solar spectrum. UVB induces mainly dipyrimidine photoproducts in DNA by a direct photochemical mechanism, whereas UVA is absorbed by other cellular constituents and induces mainly oxidative damage indirectly. The proportions of the different dipyrimidine photoproducts, and the ratio of dipyrimidine to oxidative damage depend on the exact spectral output of a UV source. Irradiation of human epidermal keratinocytes induces release of cytokines, with cyclobutane pyrimidine dimers playing a significant role in the process. These cytokines may then modulate the activity of cells of the immune system. Freshly isolated human lymphocytes are exquisitely sensitive to UVB irradiation, because of their low deoxyribonucleotide pools. They also have a separate defect in removal of cyclobutane pyrimidine dimers from their DNA. We have observed that frequencies of mutations at the hprt locus in human T-lymphocytes and translocations involving the bcl2 locus in B-lymphocytes appear to be associated with sunlight levels over the period before the blood sample was taken. This may be an indirect cytokine-mediated effect, and may be relevant to the possible link between non-Hodgkin's lymphoma and sunlight. On the other hand, sunlight can have beneficial effects, and may protect against autoimmune diseases including type I diabetes and multiple sclerosis.

The induction and activation of STAT1 by all-trans-retinoic acid are mediated by RAR beta signaling pathways in breast cancer cells

Retinoic acid receptor-beta (RAR beta) and signal transducer and activator of transcription 1 (STAT1) are important mediators of the antiproliferative and apoptotic actions of retinoids and cytokines/growth factors, respectively. Expression of both RAR beta and STAT1 is lost in most breast cancer cell lines but it can be induced by retinoids in estrogen receptor-positive cells. We investigated a possible functional connection between these two mediators and present evidence supporting RAR beta as a tumor suppressor. First, by using different receptor-selective retinoids, we demonstrated that RAR beta induction in MCF-7 cells by all-trans-retinoic acid (atRA) was associated with the activation of STAT1 gene transcription. The direct involvement of RAR beta in atRA-induced STAT1 gene activation was further demonstrated by showing that transfection with an anti-sense RAR beta construct blocked atRA-induced STAT1 expression in MCF-7 cells whereas introduction of a sense-RAR beta construct resulted in STAT1 induction by atRA in MDA-MB 231 cells. In addition, we showed that STAT1 was phosphorylated/activated under atRA treatment of MCF-7 cells; this process required the involvement of RAR beta and protein synthesis. STAT1 phosphorylation/activation was accompanied by increased tyrosine kinase activity that was not due to the activation of JAK1, JAK2 or Tyk 2, suggesting the possible involvement of an unidentified tyrosine kinase.

Frequencies of hprt(-) mutations and bcl-2 translocations in circulating human lymphocytes are correlated with United Kingdom sunlight records

Between 1983 and 1995 we have monitored human populations for evidence of exposure to environmental mutagens, taking blood samples to measure hprt(-) mutant frequency in T cells and more recently bcl-2 t(14:18) translocation frequency in B cells. We have now analysed data from 785 assays on 448 blood samples from 308 normal subjects and find that there is a highly significant statistical correlation between hprt(-) mutant frequency and the sunlight record for the 3 weeks prior to taking the blood sample. We discuss the weaknesses in retrospective studies of this nature and the possibility of spurious epidemiological correlations that may result. More controlled experiments can be envisaged that would give a firmer basis to the statistical associations observed. hprt(-) mutations in T cells show little evidence of a UV fingerprint, so that the correlation may be due to immunomodulation rather than mutation. We also find a correlation between the sunlight record and bcl-2 translocation. This translocation is found at a low frequency in the B cells of many normal subjects and is the commonest translocation observed in non-Hodgkin's lymphoma. Our results strengthen the case for a link between sunlight and this increasingly common cancer.

Signal relay by retinoic acid receptors alpha and beta in the retinoic acid-induced expression of insulin-like growth factor-binding protein-3 in breast cancer cells

Neither retinoic acid receptor-beta (RARbeta) nor insulin-like growth factor-binding protein-3 (IGFBP-3) is expressed in breast cancer cell line MCF-7. The expression of both proteins can be induced in response to all-trans-retinoic acid (atRA). By using an RARalpha-selective antagonist (Ro 41-5253), we demonstrated that RARbeta expression was induced by atRA through an RARalpha-dependent signaling pathway and that RARbeta induction was correlated with IGFBP-3 induction. However, MCF-7 cells transfected with sense RARbeta cDNA expressed IGFBP-3 even in the presence of the RARalpha-selective antagonist Ro 41-5253. On the other hand, antisense RARbeta cDNA transfection of MCF-7 cells blocked atRA-induced IGFBP-3 expression, indicating that RARbeta is directly involved in the mediation of IGFBP-3 induction by atRA. Induction of IGFBP-3 expression by atRA occurs at the transcriptional level, as measured by nuclear run-on assays. Finally, we showed that atRA-induced IGFBP-3 is functionally active in modulating the growth-promoting effect of IGF-I. These experiments indicate that RARalpha and RARbeta, both individually and together, are important in mammary gland homeostasis and breast cancer development. By linking IGFBP-3 to RARbeta, our experiments define the signal intersection between the retinoid and IGF systems in cell growth regulation and explain why loss of RARbeta might be critical in breast cancer carcinogenesis/progression.

Glucose kinetic responses to protein supplementation and exogenous somatotropin in late gestation dairy cows

Glucose kinetics were measured in late gestation multiparous Holstein dairy cows fed diets with different amounts of dietary crude protein (13.3 vs. 17.8%), with and without exogenous somatotropin. The trial was conducted as a completely randomized design; 35 cows were used in the final analysis. Kinetic measurements were made using the single injection technique with uniformly labeled 13C-labeled glucose. A diet that contained 17.8% crude protein appeared to increase glucose utilization without a corresponding increase in supply. The evidence was an increased rate of glucose disposal. In contrast, exogenous bovine somatotropin (Posilac, Monsanto Co., St. Louis, MO) appeared to enhance glucose conservation, as indicated by a tendency for a decreased fractional catabolic rate and an increased glucose pool size. Somatotropin appeared to modify glucose metabolism in a pattern favorable for supporting terminal fetal development and lactogenesis and for maintaining or enhancing maternal glycemia. The latter pattern could have implications for improving the health of periparturient dairy cows.

The 0.8% ultraviolet B content of an ultraviolet A sunlamp induces 75% of cyclobutane pyrimidine dimers in human keratinocytes in vitro

Tanning lamps, emitting predominantly ultraviolet (UV) A, are used widely throughout the U.K. and other countries, but little is known about the long-term risks associated with their use, especially with respect to skin cancer. We have exposed normal human epidermal keratinocytes to a commercial tanning lamp and used the comet assay in association with DNA repair enzymes T4 endonuclease V and endonuclease III to investigate the relative yields of directly formed cyclobutane pyrimidine dimers (CPDs) and indirectly formed types of oxidative DNA damage. To put the risk of using tanning lamps into perspective, the sunbed used in this study (five Philips Performance 80W-R UVA tubes at a distance of 35 cm) was found to be approximately 0.7 times as potent at inducing CPDs as U.K. natural sunlight around noon on a fine summer day. This compares with a relative risk for CPD induction and erythema of 0.8 and 0.7 times, respectively, calculated from the relevant action spectra of tanning lamps and British noontime sunlight. To determine the relative contribution of UVB and UVA to the induction of CPDs and oxidative DNA damage, we modified the spectral output of the tanning lamps with a series of Schott WG UVB filters. The induction of CPDs was more dependent on the UVB component of the sunbed than oxidative types of damage. Schott WG UVB filters with 50% transmission at 305 nm reduced the yield of T4 endonuclease V sites by 42% while there was only a 17% decrease in the yield of endonuclease III sites. CPD induction was not completely abolished after irradiation through WG335 and WG345 nm filters despite there being no detectable UVB. From these data, it was estimated that, although the tanning lamps emitted only 0.8% of their total output in the UVB range, these wavelengths were responsible for the induction of over 75% of CPDs and 50% of the oxidative damage to DNA.

Insulin secretion, DNA damage, and apoptosis in human and rat islets of Langerhans following exposure to nitric oxide, peroxynitrite, and cytokines

Cytokine-induced damage may contribute to destruction of insulin-secreting beta-cells in islets of Langerhans during autoimmune diabetes. There is considerable controversy (i) whether human and rat islets respond differently to cytokines, (ii) the extent to which cytokine damage is mediated by induction of nitric oxide formation, and (iii) whether the effects of nitric oxide on islets can be distinguished from those of reactive oxygen species or peroxynitrite. We have analyzed rat and human islet responses in parallel, 48 h after exposure to the nitric oxide donor S-nitrosoglutathione, the mixed donor 3-morpholinosydnonimine, hypoxanthine/xanthine oxidase, peroxynitrite, and combined cytokines (interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma). Insulin secretory response to glucose, insulin content, DNA strand breakage, and early-to-late stage apoptosis were recorded in each experiment. Rat islet insulin secretion was reduced by S-nitrosoglutathione or combined cytokines, but unexpectedly increased by peroxynitrite or hypoxanthine/xanthine oxidase. Effects on human islet insulin secretion were small; cytokines and S-nitrosoglutathione decreased insulin content. Both rat and human islets showed significant and similar levels of DNA damage following all treatments. Apoptosis in neonatal rat islets was increased by every treatment, but was at a low rate in adult rat or human islets and only achieved significance with cytokine treatment of human islets. All cytokine responses were blocked by an arginine analogue. We conclude: (i) Reactive oxygen species increased and nitric oxide decreased insulin secretory responsiveness in rat islets. (ii) Species differences lie mainly in responses to cytokines, applied at a lower dose and shorter time than in most studies of human islets. (iii) Cytokine effects were nitric oxide driven; neither reactive oxygen species nor peroxynitrite reproduced cytokine effects. (iv) Rat and human islets showed equal susceptibility to DNA damage. (v) Apoptosis was not the preferred death pathway in adult islets. (vi) We have found no evidence of human donor variation in the pattern of response to these treatments.

In search of an "Authentic" women's medicine: the strange fates of Trota of Salerno and Hildegard of Bingen

Despite centuries of debate about the medieval writers Trota and Hildegard, there still remain widely disparate views of them in both popular and scholarly discourses. Their alternate dismissal or romanticization is not due to a simple contest between antifeminist and feminist tendencies. Rather, issues of gender have intersected in varying ways with other agendas (intellectual, nationalist, etc.). Recent philological researches have helped not only to clarify why these earlier interpretations were created in the first place, but also to raise our understanding of these women and their work to a new, higher level.

c-Myc is a major mediator of the synergistic growth inhibitory effects of retinoic acid and interferon in breast cancer cells

The molecular signaling events involved in the inhibition of breast cancer cell growth by retinoic acid and interferon-alpha were investigated. All-trans-retinoic acid and interferon-alpha acted synergistically to inhibit growth of both the estrogen receptor-positive breast cancer cell line MCF-7 and the estrogen receptor-negative line BT-20. In MCF-7 cells, all-trans-retinoic acid potentiated the effects of interferon-alpha by up-regulating the expression of the RNA-dependent protein kinase (PKR). Consequently, the synergism between all-trans-retinoic acid and interferon-alpha down-regulated the expression of c-Myc, but not its functional partner, Max. Transfection of MCF-7 cells with a dominant-negative mutant of PKR relieved c-Myc down-regulation and cell growth inhibition, indicating that PKR is directly involved in c-Myc down-regulation and that c-Myc down-regulation is responsible for the inhibition of cell growth. Corresponding with c-Myc down-regulation, c-Myc.Max heterodimers bound to their consensus DNA sequence were undetectable in cells treated with all-trans-retinoic acid and interferon-alpha, indicating diminished c-Myc functionality. When c-Myc was overexpressed ectopically via a c-Myc expression vector, MCF-7 cells became resistant to growth inhibition by all-trans-retinoic acid plus interferon-alpha. These experiments define the following pathway as a major pathway in the synergistic growth inhibition of MCF-7 cells by all-trans-retinoic acid plus interferon-alpha: all-trans-retinoic acid + interferon-alpha --> upward arrow double-stranded RNA-dependent protein kinase --> downward arrow c-Myc --> cell growth inhibition.

Development of a compartmental model describing the dynamics of vitamin A metabolism in men

Model-based compartmental analysis was used with the Simulation, Analysis and Modeling (SAAM) computer programs to analyze data on plasma retinoid kinetics in adult male subjects for 7 d after a single oral dose of 105 mumol of [8,9,19-13C]retinyl palmitate. We present here the data for one subject and discuss in detail the steps taken to develop a physiologically-based compartmental model that describes the dynamic behavior of plasma retinyl esters, [12C]retinol, [8,9,19-13C]retinol, and the sum of [12C] and [13C]retinol. First an absorption model was developed to fit data on the plasma appearance and disappearance of retinyl esters; this was used as input in development of models for labeled and unlabeled retinol. The large oral load of labeled vitamin A perturbed the unlabeled tracee system, and thus parallel models for tracer and tracee were developed; and a time-variant fractional transfer coefficient was incorporated into the tracee model. Following the absorption model, four-compartment models were developed to describe the dynamics of both labeled and unlabeled retinol. These models predict that, in spite of the large vitamin A load, the absorption efficiency was 34%; hepatic (presumably parenchymal cell) processing of the absorbed dose was essentially complete by 24 h; and, by 7 days, approximately 80% of the absorbed dose was in a compartment that presumably represents stored liver retinyl esters. The model also predicts that approximately 50 mumol of retinol passed through the plasma each day, compared to an estimated utilization rate of 4 mumol/day. This project provides unique and important information about whole-body vitamin A dynamic in humans, and presents approaches to specific modeling issues that may be encountered by others.

Plasma retinol is a major determinant of vitamin A utilization in rats

We studied relationships among vitamin A intake, liver levels of vitamin A, plasma retinol concentrations and the irreversible utilization of vitamin A. To supplement existing data, we first used model-based compartmental analysis to determine vitamin A utilization and other kinetic parameters in male Sprague-Dawley rats that had adequate liver vitamin A stores ( approximately 9000 nmol) and were fed a diet containing low levels of vitamin A. Plasma retinol kinetics were monitored for 43 d after administration of [3H]retinol-labeled plasma to rats consuming approximately 23 (Group 1, n = 6) or approximately 4.2 (Group 2, n = 6) nmol vitamin A/d. Data for plasma tracer vs. time and for tracer lost irreversibly by the end of the experiment, were fit to a three-compartment model in which plasma retinol exchanges with vitamin A in two kinetically distinct extravascular compartments. Irreversible utilization rates ( approximately 41 nmol/d) were similar to those for rats that are in vitamin A balance, suggesting that, when liver vitamin A stores are adequate, utilization rate is not decreased to compensate for a low vitamin A intake. Multiple linear regression analysis was then used to relate these and previously collected data (total, 62 rats) on vitamin A intake (4. 2-49 nmol/d), plasma retinol concentration (1.4-2.5 micromol/L) and liver vitamin A level (1.2-11,000 nmol) to vitamin A utilization (disposal rate, 4.2-68 nmol/d). A significant relationship (R2(adj) = 0.93) was found for the equation [disposal rate (nmol/d) = -0.720 (nmol/d) + 0.844 (d-1).(plasma retinol; nmol) + 0.00139 (d-1).(liver vitamin A; nmol) + 0.220.(vitamin A intake; nmol/d)]. Plasma retinol accounted for 92% of the variability in disposal rate (vs. 5% for liver vitamin A and 3% for vitamin A intake). We conclude that plasma retinol is a main determinant of the irreversible utilization of vitamin A in rats with low to moderate vitamin A intake.

Growth factor protection against cytokine-induced apoptosis in neonatal rat islets of Langerhans: role of Fas

Treatment of neonatal rat islets of Langerhans with combined cytokines (interleukin-1beta 10(-10) M, tumour necrosis factor-alpha 10(-10) M, interferon-gamma 5 U/ml) led to extensive cell death, which was potentiated by Fas activation with the anti-Fas cytolytic antibody JO2. Pre-treatment with insulin (25 ng/ml) or insulin-like growth factor-1 (10(-8)M) gave only partial protection against cell killing, but prevented the Fas-mediated component. In the absence of cytokine treatment, Fas-mediated killing was not observed.

Induction of interleukin-6 production by ultraviolet radiation in normal human epidermal keratinocytes and in a human keratinocyte cell line is mediated by DNA damage

The sunburn reaction is the most common consequence of human exposure to ultraviolet radiation (UVR), and is mediated at least in part by interleukin-6 (IL-6). The aim of this study was to determine if DNA is a major chromophore involved in the induction of IL-6 following UV irradiation of a human epidermoid carcinoma cell line (KB), and of normal human epidermal keratinocytes. We first confirmed that IL-6 release was associated with enhanced levels of IL-6 mRNA transcripts. The wavelength dependence for IL-6 release was then investigated by irradiating the cells at defined wavelengths (254, 302, 313, 334, and 365 nm) with a monochromator. The maximum effect on IL-6 release was observed at 254 nm with only low levels of induction observed at wavelengths above 313 nm. The wavelength dependence for UV-induced IL-6 release was similar to that for DNA absorption or for the induction of cyclobutane pyrimidine dimers (CPD). To determine whether UV-induced DNA damage mediated IL-6 secretion, the role of CPD was investigated by treating keratinocytes with photosomes (photolyase encapsulated in liposomes) followed by photoreactivating light. This photoreversal procedure led to a reduction in the levels of the UVC-induced secretion of IL-6, which in normal human keratinocytes was unambiguously associated with repair of CPD. We conclude that the release of IL-6 from human keratinocytes following short-wave UVC and UVB irradiation is mediated by DNA damage and that CPD play an important role in this process.

Plasma thyroid hormone kinetics are altered in iron-deficient rats

Iron deficiency anemia is associated with lower plasma thyroid hormone concentrations in rodents and, in some studies, in humans. The objective of this project was to determine if plasma triiodothyronine (T3) and thyroxine (T4) kinetics were affected by iron deficiency. Studies were done at a near-thermoneutral temperature (30 degrees C), and a cool environmental temperature (15 degrees C), to determine plasma T3 and T4 kinetics as a function of dietary iron intake and environmental need for the hormones. Weanling male Sprague-Dawley rats were fed either a low Fe diet [iron-deficient group (ID), <5 microg/g Fe] or a control diet [control group (CN), 35 microg/g Fe] at each temperature for 7 wk before the tracer kinetic studies. An additional ID group receiving exogenous thyroid hormone replacement was also used at the cooler temperature. For T4, the disposal rate was >60% lower (89 +/- 6 vs. 256 +/- 53 pmol/h, P < 0.001) in ID rats than in controls at 30 degrees C, and approximately 40% lower (192 +/- 27 vs. 372 +/- 26 pmol/h, P < 0.01) in ID rats at 15 degrees C. Exogenous T4 replacement in a cohort of ID rats at 15 degrees C normalized the T4 concentration and the disposal rate. For T3, the disposal rate was significantly lower in ID rats in a cool environment (92 +/- 11 vs. 129 +/- 11 pmol/h, P < 0.01); thyroxine replacement again normalized the T3 disposal rate (126 +/- 12 pmol/h). Neither liver nor brown fat thyroxine 5'-deiodinase activities were sufficiently different to explain the lower T3 disposal rates in iron deficiency. Thus, plasma thyroid hormone kinetics in iron deficiency anemia are corrected by simply providing more thyroxine. This suggests a central regulatory defect as the primary lesion and not peripheral alterations.

Repair of cyclobutane pyrimidine dimers in unstimulated human mononuclear cells is deficient at very low fluences of ultraviolet B and is not enhanced by addition of deoxyribonucleosides

Unstimulated human T lymphocytes are exquisitely sensitive to UVB irradiation. This hypersensitivity appears to relate to low deoxyribonucleotide pool sizes. They have also been reported to be defective in global excision of cyclobutane pyrimidine dimers, but such experiments may have been carried out at supralethal doses, where unrepaired excision breaks persist indefinitely. We use a T4 endonuclease Comet assay to show that removal of cyclobutane pyrimidine dimers is defective in the unstimulated mononuclear cell fraction (mainly T lymphocytes) even at sublethal fluences from an FS20 broad spectrum UVB lamp. Moreover, removal is not enhanced by addition of deoxyribonucleosides to the medium. Cells which are failing to remove cyclobutane pyrimidine dimers readily form fresh incision breaks in response to a second UVB fluence, indicating that they retain repair capacity and suggesting that removal of types of damage other than cyclobutane pyrimidine dimers is effective.

Use of model-based compartmental analysis to study effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on vitamin A kinetics in rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic, widespread environmental contaminant that has dramatic adverse effects on the metabolism of vitamin A. We used model-based compartmental analysis to investigate sites and quantitative impacts of TCDD on vitamin A kinetics in rats given on oral loading dose of TCDD in oil (3.5 micrograms/kg) followed by weekly maintenance doses (0.7 microgram/kg) or oil only. [3H]Retinol in its plasma transport complex (experiment 1) of lymph containing chylomicrons labeled mainly with [3H]retinyl esters (experiment 2) were administered i.v., and tracer kinetics in plasma, liver, carcass, urine, and feces were measured for up to 42 days. TCDD treatment caused significant reductions in liver vitamin A levels and significant changes in tracer kinetics and tracer excretion. A four-compartment model was used to fit tracer data for experiment 1; for experiment 2, compartments were added to describe the metabolism of newly absorbed vitamin A. The compartmental models predict that TCDD caused a slight delay in plasma clearance (via an increased recycling to plasma), and in liver processing, of chylomicron-derived vitamin A. Models for both experiments predict that TCDD exposure did not affect the fractional uptake of plasma retinol from the rapidly turning-over extravascular pool, but it doubled the fractional transfer of recycled retinol from slowly turning-over pools of vitamin A to plasma. The residence time for vitamin A was reduced by 70% in TCDD-treated rats, transfer into urine and feces was tripled, and vitamin A utilization rates were significantly increased. Since our results do not indicate that retinol esterification is inhibited, we hypothesize that some of the significant effects of TCDD on vitamin A metabolism result from increased catabolism and mobilization of vitamin A from slowly turning-over pools (especially the liver).

Factors affecting the DNA damaging activity of superoxide and nitric oxide

Nitric oxide and superoxide are formed endogenously and can react with each other and with other molecules to form a range of secondary and tertiary products. Some of these (e.g., peroxynitrite) are potent DNA-damaging agents and others (e.g., S-nitrosoglutathione) can act as reservoirs of the reactive species. Although the chemistry of these processes is now becoming understood, the question of which products are significant in vivo is not necessarily clear. To investigate these processes we have developed a cell-free version of the Comet assay, where the DNA from isolated nuclei is treated in agar on a microscope slide, following lysis. This offers an exceptionally sensitive assay for strand breakage in free DNA. Despite being present as a scavenger in the cell at millimolar levels, glutathione can act as a DNA-damaging pro-oxidant. Under appropriate conditions, glutathione-mediated damage is suppressed by superoxide dismutase and we suggest that superoxide may be a direct damaging agent, whose activity can be masked because of the involvement of superoxide in indirect mediation of damage or because of concomitant presence of hydroxyl radical.

Use of the Comet assay to investigate the role of superoxide in glutathione-induced DNA damage

Although glutathione is an important scavenging molecule within the cell, it can also act as a pro-oxidant and at biological concentrations (1 mM) can induce DNA damage. We have used a sensitive cell-free Comet assay for DNA strand breakage to investigate this damage and to try to determine the active species involved. We show a substantial protection against glutathione-mediated DNA damage by superoxide dismutase (200 U/ml) and complete protection by combined superoxide dismutase and catalase. Damage is also prevented by EDTA but only at 100 mM and is not prevented by the chelating agent diethylenetriamine-pentaacetic acid (100 microM). Although superoxide is known to potentiate DNA damage by other reactive species, none of these indirect mechanisms seem to account for our results and it is possible that superoxide may damage DNA directly. Under the same experimental conditions, S-nitrosoglutathione requires ultraviolet A photolysis to cause DNA strand breakage and superoxide dismutase increases the level of this damage. When intact human lymphocytes are incubated with glutathione (1 mM) in phosphate buffer, DNA damage is also observed, but in this case it is completely preventable by catalase, with no protective effect of superoxide dismutase. Since cellular scavenging systems are not completely protective against reactive species formed from autooxidation of extracellular glutathione and since glutathione and oxygen are ubiquitously present within cells, our results imply that cells may have a mechanism of preventing autooxidation, rather than simply relying on scavenging the reactive species formula.

Induction of mutagenic DNA damage in human fibroblasts after exposure to artificial tanning lamps

There is increasing concern about the adverse health effects associated with the use of sunbeds, particularly with respect to skin photocarcinogenesis. The induction of mutagenic DNA damage is a prerequisite for the development of skin tumours, and it is well established that direct types of damage such as cyclobutane pyrimidine dimers (CPDs) give rise to mutations in tumour suppressor genes and oncogenes. In addition, ultraviolet radiation may induce indirect types of DNA damage, including oxidative products, which are also potentially mutagenic. By using specific DNA repair enzymes (T4 endonuclease V and endonuclease III) and the comet assay we have been able to detect the induction of CPDs, oxidized or hydrated pyrimidine bases and single-strand breaks in cultured human fibroblasts (MRC-5) after exposure for between 15 s and 20 min on two different commercial sunbeds containing Philips 'Performance' 100W-R or Philips TL80W/10R lamps. The ratio of endonuclease III to T4 endonuclease V sensitive sites varied substantially between the two lamps and was 3.3% and 18%, respectively. The sunbed containing the 'Performance' 100W-R lamps was as potent at inducing CPDs as was natural sunlight in fine weather. These results establish that commercial tanning lamps produce the types of DNA damage associated with photocarcinogenesis in human cells, and complement epidemiological evidence indicating the potential risk of using sunbeds.

Use of the comet assay to investigate possible interactions of nitric oxide and reactive oxygen species in the induction of DNA damage and inhibition of function in an insulin-secreting cell line

We have previously used the comet assay to demonstrate that the nitric oxide donor 3-morpholinosydnonimine (SIN-1) produces DNA damage in rat islets of Langerhans and in the SV40-transformed insulin-secreting hamster cell line, HIT-T15. Damage is not prevented by the addition of superoxide dismutase (SOD). In the present study, we have compared SIN-1, which generates nitric oxide, superoxide anion and hydrogen peroxide, with two other nitric oxide donors, S-nitrosoglutathione (GSNO) and the tetra-iron-sulphur cluster nitrosyl, Roussin's black salt (RBS). We have used the comet assay as a highly sensitive method to measure DNA-damaging ability, and also measured inhibition of DNA synthesis and inhibition of insulin secretion. We have examined the effect of SOD and catalase on each of these endpoints in HIT-T15 cells following a 30-min exposure to the compounds (24 h for DNA synthesis). All compounds produced a significant dose-dependent increase in strand-breakage formation and all inhibited DNA synthesis and glucose-stimulated insulin secretion. RBS was the most potent. SOD did not reduce the responses observed with any of the compounds. Catalase largely prevented DNA strand breakage, inhibition of DNA synthesis and inhibition of insulin secretion by SIN-1, but had no effect on responses to GSNO or RBS. Addition of SOD together with catalase gave no greater protection against SIN-1 than catalase alone. The nitric oxide and superoxide anion produced by SIN-1 are though to combine to form highly reactive peroxynitrite. In addition, H2O2 may be formed in the presence of SIN-1 and may form hydroxyl radical in the presence of a transition metal, such as Fe2+. It appears that in insulin-secreting cells, the effects of SIN-1 are largely mediated by this latter mechanism. In contrast, GSNO and RBS appear to act by a different mechanism, not overtly involving reactive oxygen species. GSNO and H2O2 show no significant interaction in the induction of DNA strand breaks. Both nitric oxide and H2O2 are effective, directly or indirectly, as DNA strand-breaking agents, inhibitors of DNA synthesis and inhibitors of insulin secretion.

N-3 fatty acids and chylomicron metabolism in the rat

Dietary n-3 fatty acids (FAs) reduce postprandial triacylglycerol concentrations in humans by unknown mechanisms. Our goals were to reproduce this phenomenon in the rat, and then to determine the mechanism. In an oral fat tolerance study two groups of rats were fed diets containing 2.1% ethyl esters of n-3 FA or olive oil for 2 weeks. After gavaging with emulsified soybean oil, the postprandial chylomicron triacylglycerol levels in the n-3 FA group were reduced by 40% (P < 0.05). The hypothesis that n-3 FA feeding reduced chylomicron production/secretion from the gut was tested by blocking chylomicron removal with Triton WR1339 before gavaging the rats with the fat load. This completely eliminated the hypochylomicronemic effect suggesting that chylomicron input was not inhibited by n-3 FAs. Chylomicron clearance was studied by injecting chylomicrons containing radioactive retinyl esters and triacylglycerol into rats from both groups. Pre-feeding with n-3 FAs accelerated the removal of chylomicron triacylglycerol and retinyl esters from the plasma with significantly lower fractions of dose remaining at 2, 4, and 8 min post-injection for both tracers. These findings suggest than n-3 FAs reduce postprandial chylomicronemia in the rat by accelerating chylomicron lipid clearance.

Hypersensitivity of ataxia-telangiectasia fibroblasts to a nitric oxide donor

Ataxia-telangiectasia (A-T) is a human autosomal recessive disease characterised by immunodeficiency, extreme sensitivity to ionising radiation and progressive cerebellar ataxia. The defective gene has recently been cloned and is a member of the phosphatidylinositol 3-kinase family. We have investigated the possibility that the neurodegeneration in A-T might be induced by an endogenously formed mutagen causing radiation-like damage. Nitric oxide is known to be formed in the cerebellum and we present evidence that A-T fibroblasts are hypersensitive to killing by the nitric oxide donor S-nitrosoglutathione (GSNO), as are fibroblasts from a radiosensitive individual without ataxia. Killing was determined as loss of colony forming ability. GSNO induces dose-dependent DNA strand breakage, but to no greater extent in A-T fibroblasts. Breakdown of GSNO to nitrite and nitrate appears to occur to the same extent in both normal and A-T fibroblasts. Cell killing by GSNO appears to be associated in both types of cell with formation of nitrite, rather than nitrate, as the ultimate oxidation product of nitric oxide.

Biomonitoring of possible human exposure to environmental genotoxic chemicals: lessons from a study following the wreck of the oil tanker Braer

In January 1993 the oil tanker Braer ran aground in the Shetland Islands, Scotland. Approximately 80,000 tons of crude oil were released. Exceptionally high winds caused extensive pollution and exposure of the local population to crude oil. We describe the study which was immediately set in place to examine the exposed population for evidence of genotoxic exposure. Blood samples were taken and primary DNA damage was measured in the mononuclear cell fraction by the butanol modification of the 32P-postlabelling method. Mutation was measured at the hprt locus in T lymphocytes. No evidence of genotoxicity was obtained for either end point, but nevertheless, we believe that useful lessons were learnt, which should be incorporated into the design of future studies: (1) A rapid response is essential, and even if sufficient funds are not immediately available, it is still worth attempting to obtain samples quickly and use cryopreservation, also to attempt to estimate exposure. (2) Adequate numbers of volunteers must be sought, together with enough controls, not just to allow meaningful analysis but to overcome loss of samples and failure of things to go according to plan. (3) Points concerning laboratory practice include: (i) samples should be coded, (ii) clearly defined and proven protocols should be used, (iii) irreplaceable samples should not be used for method development, (iv) should a problem become apparent during the study, work on such samples should cease immediately until the problem is solved, (v) all critical experimental components should be pretested against a laboratory standard. (4) The study design should include replicate experiments to monitor experimental variability and reproducibility, as well as internal standards and cryopreserved "in house" samples. Care must be taken that samples from any one exposure group are spread between a number of independent experiments and that each experiment includes samples from a number of exposure groups. (5) A computerised data base should be maintained with full details of experimental variables, donor attributes, and raw data so that any contribution of experimental artefacts to "outlier" results can be monitored. (6) Because of the nature of the statistical variation for many environmental genotoxicity end points, only a large-scale study is likely to be capable of yielding useful information.

Correlated mutagenesis of bcl2 and hprt loci in blood lymphocytes

In vivo measurement of human somatic mutations may be a valuable biodosimeter of exposure to carcinogens and of cancer risk. We have surveyed translocations at the bcl2 locus in B lymphocytes, and mutations at hprt in T lymphocytes, in 120 individuals with varying exposure to radon and cigarette smoke. bcl2 t(14:18) translocation is the commonest chromosomal alteration observed in non-Hodgkins lymphoma (NHL). We observed a significantly larger range of bcl2 translocation frequency (range: 0-372 x 10(-6), median: 1.9 x 10(-6)) than of hprt mutation frequency (range: 0-76.4 x 10(-6), median: 11.1 x 10(-6)), which is likely the result of clonal proliferation of deathless B cell mutants. We observed that the frequencies of these two distinct lymphocytic mutations are significantly correlated. Although some of the correlated variation is explained by age, a significant correlation of bcl2 mutagenesis persists after age adjustment. Correlated mutagenesis at distinct loci in distinct cell types could be explained by the existence of a mutator phenotype or by variation in exposure to environmental mutagens. NHL is commoner in men than in women, and our data indicate a trend toward higher bcl2 mutagenesis in males than females. There is mounting epidemiological evidence for a worldwide increase in NHL, which may have an environmental basis; molecular epidemiological analysis of bcl2 mutagenesis in exposed populations might be especially relevant to the identification of putative environmental causes. Given the relative ease of the bcl2 assay versus the hprt assay, and the consistency with which data are reproduced from laboratory to laboratory, it is likely that the bcl2 assay will be soon added to the array of assays used in human mutational surveillance.

Influence of environmental and genetic factors on variation in human response to DNA damaging agents

Exogenous DNA damaging agents must be considered in the context of endogenous reactive species which have the potential to damage DNA. Although a no-effect level for a DNA-damaging compound may not exist, it may be feasible to define a level where reducing exposure to the compound is no longer the most effective way of reducing human risk. Modifying environmental factors which affect human response to damage may be the better strategy. Although a number of rare human syndromes are associated with a reduced ability to repair DNA damage, it is not clear how wide is the range of genetic variation in repair capacity among normal individuals. Studies with DNA repair-deficient human syndromes indicate that processes other than mutation and DNA repair must be involved in the development of cancer, and these processes may represent new sources of variation in human response to genotoxic agents.

Inhibition of RNA and DNA synthesis in UV-irradiated normal human fibroblasts is correlated with pyrimidine (6-4) pyrimidone photoproduct formation

UV-irradiation of living cells results in an inhibition of RNA and DNA synthesis. The purpose of this study was to determine whether specific photoproducts or the total combined yield of lesions were responsible for these effects. Asynchronously dividing human fibroblasts from normal donors were irradiated with UVC (254 nm), broad spectrum UVB (290-320 + nm, Westinghouse FS20 lamp) or narrow spectrum UVB (310-315 nm, Philips TL01 lamp) at fluences which induce known yields of cyclobutane pyrimidine dimers, pyrimidine (6-4) pyrimidone photoproducts or Dewar isomers. DNA synthesis was approximately 3-4 times more sensitive to both UVC and UVB irradiation than RNA synthesis. The immediate inhibition of RNA and DNA synthesis was correlated with (6-4) rather than overall photoproduct formation suggesting that the (6-4) photoproduct is the mediator of these inhibitory effects. In support of this suggestion we found that photoreactivation of cells cultured from the marsupial, mouse Sminthopsis crassicaudata, resulted in removal of 70% of pyrimidine dimers from the overall genome, but had only a slight effect on the recovery of RNA synthesis.

Nitric oxide donors decrease the function and survival of human pancreatic islets

Nitric oxide (NO) has been proposed as a possible mediator of beta-cell damage in human IDDM. This hypothesis is based on in vitro studies with rodent pancreatic islets. In the present study we examined whether human beta-cells are affected by NO. In view of species differences in beta-cell sensitivity to damaging agents, rat islets were investigated in parallel. Isolated islets were exposed for 90 min to different concentrations of three chemically unrelated NO donors, SIN-1, GSNO or RBS. At the end of this incubation, human insulin release was mostly similar in control and NO-treated islets but, 48 h later, islet retrieval, islet DNA and insulin content, and glucose-induced insulin release were markedly lower in islets exposed to NO donors. Rat islets were already inhibited during the initial 90 min; 48 h later their loss in beta-cell function was similar to that in human islets. Nicotinamide or succinic acid monomethyl ester partially protected against SIN-1 induced islet cell loss, but not against the functional inhibition of human pancreatic islets. Exposure of human or rat islets to RBS was associated with significant DNA strand breakage, as judged by the comet assay (single cell gel electrophoresis) and by ultrastructural signs of cell damage. DNA damage was more severe in rat islet cells exposed to similar amounts of RBS. It is concluded that NO donors can damage human pancreatic islets, an effect paralleled by induction of nuclear DNA strand breaks.