Biomedical subjects

L L Smith

Publications and source records attributed to L L Smith.

At least 37 records · Page 2Linked to original sources

PubMed2000

Tissue distribution of 2-(2-nitro-4-trifluoromethylbenzoyl)-cyclohexane-1,3-dione (NTBC) and its effect on enzymes involved in tyrosine catabolism in the mouse.

Administration of a single oral dose of 2-(2-nitro-4-trifluoromethyl-benzoyl)-cyclohexane-1,3-dione (NTBC) to mice increases the concentration of tyrosine in the plasma and aqueous humour. The tyrosinaemia is both time and dose-dependent with a single dose of 30 micromol NTBC/kg (10 mg/kg) producing maximal concentrations of tyrosine in plasma of about 1200 nmol/ml and in aqueous humour of about 2200 nmol/ml at 16 h after dosing. Analysis of the key hepatic enzymes involved in tyrosine catabolism, following a single dose of 30 micromol NTBC/kg, showed that 4-hydroxyphenylpyruvate dioxygenase (HPPD) was markedly inhibited soon after dosing and that the activity recovered very slowly. In response to the tyrosinaemia, the activity of hepatic tyrosine aminotransferase (TAT) was induced about two-fold, while the activity of hepatic homogentisic acid oxidase (HGO) was reduced at 4 and 5 days after dosing. Daily oral administration of NTBC at doses up to 480 micromol NTBC/kg (160mg/kg/day) to mice produced a maximal tyrosinaemia of about 600-700nmol/ml plasma, showing some adaptation relative to a single dose. Unlike the rat, no treatment-related corneal lesions of the eye were seen at any dose levels up to 6 weeks. Administration of a single oral dose of [14C]-NTBC at 30 micromol/kg led to selective retention of radiolabel in the liver and to a lesser extent the kidneys. Our studies show that NTBC is a potent inhibitor of mouse liver HPPD, which following repeat exposure produces a marked and persistent tyrosinaemia, which does not result in ocular toxicity.

4-Hydroxyphenylpyruvate Dioxygenase↗

PubMed2000

Mobile and localized protons: a framework for understanding peptide dissociation.

Protein identification and peptide sequencing by tandem mass spectrometry requires knowledge of how peptides fragment in the gas phase, specifically which bonds are broken and where the charge(s) resides in the products. For many peptides, cleavage at the amide bonds dominate, producing a series of ions that are designated b and y. For other peptides, enhanced cleavage occurs at just one or two amino acid residues. Surface-induced dissociation, along with gas-phase collision-induced dissociation performed under a variety of conditions, has been used to refine the general 'mobile proton' model and to determine how and why enhanced cleavages occur at aspartic acid residues and protonated histidine residues. Enhanced cleavage at acidic residues occurs when the charge is unavailable to the peptide backbone or the acidic side-chain. The acidic H of the side-chain then serves to initiate cleavage at the amide bond immediately C-terminal to Asp (or Glu), producing an anhydride. In contrast, enhanced cleavage occurs at His when the His side-chain is protonated, turning His into a weak acid that can initiate backbone cleavage by transferring a proton to the backbone. This allows the nucleophilic nitrogen of the His side-chain to attack and form a cyclic structure that is different from the 'typical' backbone cleavage structures.

Amino Acid Sequence↗

PubMed2000

Cytokines and cell adhesion molecules associated with high-intensity eccentric exercise.

Unaccustomed, eccentrically biased exercise induces trauma to muscle and/or connective tissue. Tissue damage activates an acute inflammatory response. Inflammation requires the effective interaction of different physiological and biological systems. Much of this is coordinated by the de novo synthesis of families of protein molecules, cytokines. The purpose of the present paper was to determine changes in blood levels of various cytokines in response to exercise-induced muscle damage that was effected using high-intensity eccentric exercise. Six healthy, untrained, college-age male subjects were required to perform the eccentric phase of a bench press and a leg curl (4 sets, 12 repetitions/set) at an intensity equivalent to 100% of their previously determined one-repetition maximum. Samples of blood were drawn at the following times: before exercise and 1.5, 6, 12, 24, 48, 72, 96, 120, and 144 h after exercise. These samples were analyzed for interleukins (IL): IL-1beta, IL-6, and IL-10; tumor necrosis factor-alpha; colony stimulating factors (CSF): granulocyte-CSF, macrophage-CSF, and GM-CSF; for cell adhesion molecules (CAM): P- and E-selectin, and intercellular cell adhesion molecule (ICAM-1), and vascular cell adhesion molecule (VCAM-1). Results were analyzed using a repeated-measures analysis of variance (P = 0.05). Compared to baseline values, IL-1beta was reduced (P = 0.03) at 6, 24, and 96-144 h after exercise; IL-6 was elevated (P = 0.01) at 12, 24, and 72 h after exercise; IL-10 was elevated (P = 0.009) between 72 and 144 h after exercise; M-CSF was elevated (P = 0.005) at 12 and 48-144 h after exercise; and P-selectin was reduced (P = 0.01) between 24 and 144 h after exercise. It is concluded that when high-intensity eccentric exercise is compared to strenuous endurance exercise, post-exercise changes in cytokines do occur, but they are generally of a smaller magnitude, and occur at a later time period after the termination of exercise.

Adult↗

PubMed2000

The persistent efficacy of doramectin pour-on against biting and sucking louse infestations of cattle.

A repeated-exposure challenge model was used to evaluate the pour-on formulation of doramectin in preventing the establishment of louse infestations in cattle. Twenty calves cleared of preexisting biting and sucking louse infestations were randomly and equally allocated to either a doramectin-treated or untreated control group, with five replicates per group. Doramectin pour-on was administered topically at a dose rate of 500 microg/kg body weight. Every 14 days, from a pool of seeder calves with infestations of at least 50 biting and 50 sucking lice each, 10 calves were selected and 1 was placed in each replicate pen. Every week during the 112-day study, 9 predilection sites on the doramectin-treated and untreated calves were examined to estimate the louse population density. A calf met the infestation criterion for a louse species when two or more live lice were counted on two or more body regions for two consecutive count days. Because only 4 of 10 untreated calves acquired Solenopotes capillatus infestations, the persistent efficacy of doramectin against S. capillatus was not evaluated. Bovicola bovis and Linognathus vituli infestations in the untreated calves developed shortly after exposure to infested seeder calves. The acquisition of B. bovis and L. vituli infestations in the doramectin-treated group was delayed for 77 days and 105 days, respectively.

Administration, Topical↗

PubMed2000

Language lateralization and handedness in women prenatally exposed to diethylstilbestrol (DES).

Hand preferences and language lateralization were assessed in women exposed prenatally to the synthetic estrogen, diethylstilbestrol (DES), and in their unexposed sisters. The DES-exposed women showed an increased degree of hand preference (regardless of direction) and were more likely to be left handed for writing. However, the groups did not differ significantly on a dichotic listening measure of language lateralization. Perhaps as a result of the alterations in hand preferences, the typical relationship between hand preferences and language lateralization was disrupted in the DES-exposed group. Also, within the DES-exposed group, exposure early in gestation correlated with left handedness whereas exposure late in gestation correlated with reduced left ear (right hemisphere) scores on the verbal dichotic task. Results are discussed in terms of theoretical perspectives predicting hormonal influences on sexual differentiation of hemispheric asymmetry and in terms of separate critical periods for hormonal effects on individual sexually differentiated characteristics.

Adolescent↗

PubMed2000

Response of males and females to high-force eccentric exercise.

It has previously been shown that females incur less muscle damage than males after strenuous exercise, but limited data are available for humans. To determine possible differences between the sexes in humans, the response to high-force eccentric exercise was examined in a large sample of women (n = 83) and men (n = 82). The participants performed a bout of eccentric exercise of the elbow flexors consisting of 70 maximal repetitions. Isometric strength, resting elbow angle and muscle soreness were measured before, immediately after (except soreness) and then daily for 7 days after exercise. There was a significant loss in strength among both groups (69% for women and 63% for men) (P < 0.01) immediately after exercise; at 168 h post-exercise, women still had a 27% strength loss and men had a 24% strength loss. No significant difference in strength loss or recovery rate was found between men and women. Soreness reached peak values 32-48 h post-exercise (P < 0.01), with no significant difference between men and women. Range of motion decreased significantly until 3 days after exercise (14.6 degrees or 0.255 rad loss for women; 12.2 degrees or 0.213 rad loss for men) (P < 0.01); at 168 h post-exercise, the women and men still showed a loss of 4.8 degrees (0.084 rad) and 4.0 degrees (0.07 rad), respectively. There was a significant interaction of sex x time (P < 0.01); a post-hoc test indicated that the women experienced a greater loss in range of motion at 72 h than men and this difference was maintained to 168 h post-exercise (P < 0.01). Thus, our results do not support the contention that women have a lower response to eccentric exercise than men.

Adult↗

PubMed2000

Chemoprevention of breast cancer by tamoxifen: risks and opportunities.

The antiestrogen tamoxifen is widely used in the adjuvant therapy of breast cancers in women and helps to prevent the occurrence of breast tumors in healthy women. However, epidemiological studies have shown tamoxifen treatment to be associated with a 2- to 5-fold increased risk of endometrial cancer. In rats but not in mice, long-term administration of tamoxifen results in an increase in hepatocellular carcinomas. Mechanistically, this occurs through metabolic activation of the drug, mainly by the CYP3A family, to an electrophilic species, that causes DNA damage in target tissues, and subsequently leads to gene mutations. It is controversial whether low levels of DNA damage occur in human uterine tissues, and there is no evidence that this can be causally related to the mechanisms of carcinogenesis. In healthy women, the risk:benefits for the use of tamoxifen is in part related to the risk of developing breast cancer. The results from the carcinogenicity studies in rats do not predict the likelihood that women will develop liver cancer or indeed cancers in other organs. The mechanism of endometrial cancer in women remains unresolved, but the experience with tamoxifen has highlighted the potential problems that need to be addressed in the assessment of future generations of selective estrogen receptor modulators.

Animals↗

PubMed2000

Cytokine hypothesis of overtraining: a physiological adaptation to excessive stress?

Overtraining syndrome (OTS) is a condition wherein an athlete is training excessively, yet performance deteriorates. This is usually accompanied by mood/behavior changes and a variety of biochemical and physiological alterations. Presently, there is no global hypothesis to account for OTS. The present paper will attempt to provide a unifying paradigm that will integrate previous research under the rubric of the cytokine hypothesis of overtraining. It is argued that high volume/intensity training, with insufficient rest, will produce muscle and/or skeletal and/or joint trauma. Circulating monocytes are then activated by injury-related cytokines, and in turn produce large quantities of proinflammatory IL-1beta, and/or IL-6, and/or TNF-alpha, producing systemic inflammation. Elevated circulating cytokines then co-ordinate the whole-body response by: a) communicating with the CNS and inducing a set of behaviors referred to as "sickness" behavior, which involves mood and behavior changes that support resolution of systemic inflammation: b) adjusting liver function, to support the up-regulation of gluconeogenesis, as well as de novo synthesis of acute phase proteins, and a concomitant hypercatabolic state; and c) impacting on immune function. Theoretically, OTS is viewed as the third stage of Selye's general adaptation syndrome, with the focus being on recovery/survival, and not adaptation, and is deemed to be "protective," occurring in response to excessive physical/physiological stress. Recommendations are made for potential markers of OTS, based on a systemic inflammatory condition.

Acute-Phase Proteins↗

PubMed2000

Susceptibility of elk to lungworms from cattle.

Two studies were conducted to determine the infectivity of the lungworm, (Dictyocaulus viviparus) of cattle origin, in Rocky Mountain elk (Cervus elaphus nelsoni) or wapiti. In the first study, each of three 9-mo-old elk was administered 3,000 D. viviparus larvae from cattle using a nasogastric tube. In the second study, four 16-mo-old elk were each inoculated with 2,000 D. viviparus from cattle using a nasogastric tube. Elk were observed daily for signs of respiratory disease, and fecal samples were collected during the studies and evaluated for lungworm larvae using a modified Baermann technique. One elk was euthanatized during the patent period for recovery of adult lungworms, and three elk were euthanatized after larvae were no longer detected in feces. Lungworm larvae were not detected before inoculation in any of the 16-mo-old elk, but were detected 22 days after inoculation in one elk, 23 days after inoculation in two elk and 24 days after inoculation in all four elk. The prepatent period of this cattle isolate of D. viviparus in elk is therefore 22 to 24 days. The precise prepatent period was not determined in the three 9-mo-old elk, but larvae were detected in all three elk 25 days after inoculation. Numbers of larvae ranged from 1/ to 101/g feces with peak larval detection occurring 32 to 50 days after inoculation. Elk shed larvae from 22 to 83 days after inoculation, and patent periods of the parasite ranged from 24 to 62 days. Clinical signs of respiratory disease, with the exception of mild coughing after exercise, were not observed during the infections. Results from this experiment indicated that D. viviparus larvae of cattle origin can mature in elk and larvae can be passed in large numbers in feces, but this cattle isolate of D. viviparus was not highly pathogenic in elk.

Animals↗

PubMed1999

CD44 is not an adhesive receptor for osteopontin.

Osteopontin is a secreted glycoprotein with adhesive and migratory functions. Cellular interactions with osteopontin are mediated through integrin receptors which recognize the RGD domain. Recently, CD44, a non-integrin, multifunctional adhesion molecule was identified as an osteopontin receptor. CD44 is a ubiquitous surface molecule that exists as a number of different isoforms, generated by alternative splicing. To analyze which forms of CD44 mediate binding to osteopontin, we used the standard form of CD44 as CD44-human immunoglobulin fusion proteins and several splice variants in enzyme-linked immunosorbant assays. Multiple preparations of osteopontin were used including native osteopontin derived from smooth muscle cells, human urinary osteopontin, full-length recombinant osteopontin, and two recombinant osteopontin fragments expected to be formed following thrombin cleavage. Our data show that although the CD44-hlg fusion proteins could interact with hyaluronic acid as expected, there was no interaction between CD44H, CD44E, CD44v3,v8-v10, or CD44v3 with osteopontin. These studies suggest that CD44-osteopontin interactions may not be common in vivo and may be limited to a specific CD44 isoform(s), and/or a particular modified form of osteopontin.

Animals↗

PubMed1999

Tamoxifen induces G:C-->T:A mutations in the cII gene in the liver of lambda/lacI transgenic rats but not at 5'-CpG-3' dinucleotide sequences as found in the lacI transgene.

Tamoxifen, a rat liver carcinogen, can induce mutations in the lacI gene in the livers of lambda/lacI transgenic rats. However, the presence of persistent tamoxifen adducts on the liver DNA raises the possibility that some contribution to the mutagenesis from ex vivo mutations during the in vitro lacI assay cannot be ruled out. To address this issue, mutagenesis at the cII gene of the transgenic shuttle vector was determined using a selection based assay which is unaffected by the presence of tamoxifen-DNA adducts. Female lambda/lacI transgenic rats were dosed orally with tamoxifen (20 mg/kg body wt) daily for 6 weeks, causing a 3.2-fold increase in the mutant frequency (MF) in the cII gene compared with that obtained with solvent treated animals. This was similar to the MF found previously at the lacI gene and confirms that tamoxifen is mutagenic in vivo. The major class of mutation induced by tamoxifen in the cII gene was G:C-->T:A transversions as was found previously in the lacI gene. However, in the one unreplicated study of mutations in the p53 gene of liver tumours induced by tamoxifen, no G:C-->T:A transversions were found; possible differences between mutagenesis in normal and tumour tissues are explored. The major proportion of the G:C-->T:A transversions occurred at 5'-CpG-3' dinucleotide (CpG) sites in the lacI gene, but not at such sites in the cII gene. The methylation of CpG sites greatly enhances the targeting of deoxyguanosine by carcinogens, thus this finding might be explained by differences in the methylation patterns at their respective CpG sites; however, nothing is known about the methylation status of either the lacI nor the cII gene in this transgenic rat. This study raises the important issue of which target genes (mammalian or transgenic) should be used as endpoints in mammalian mutagenesis assays.

Aflatoxin B1↗

PubMed1999

Compartmentalized uterotrophic effects of tamoxifen, toremifene, and estradiol in the ovariectomized Wistar (Han) rat.

The comparative uterotrophic responses of ovariectomized Wistar (Han) rats to tamoxifen, toremifene, and 17beta-estradiol have been determined over a period of 72 h. Uterine wet weight; luminal epithelial cell hypertrophy; and BrdU labeling index in the different tissue compartments of the uterus, and the immunohistochemical expression of nuclear estrogen receptor alpha (nERalpha), and nuclear progesterone receptor (nPR) were examined. Luminal epithelial cell hypertrophy was produced by all three compounds to a similar degree. 17beta-Estradiol produced an increase in uterine wet weight due to fluid imbibition over the 3-day period, and an increase in DNA synthesis in the endometrial stromal and myometrial compartments of the uterus, as measured by increased BrdU incorporation. Estradiol increased the expression of nERalpha and nPR in the myometrium with time and decreased nERalpha levels from the overexpressed levels in control ovariectomized rat luminal epithelial cells. Tamoxifen and toremifene caused a smaller increase in uterine weight and the BrdU labeling index in the endometrial stroma and myometrium than did estradiol, and they increased the expression of nERalpha and nPR in the myometrium. Tamoxifen and toremifene differed from estradiol in that they did not decrease the expression of nERalpha in the luminal epithelial cells of the uterus. The response of PR expression was the same for tamoxifen, toremifene, and estradiol, and was therefore considered to be the most reliable indication of an estrogen-agonist effect in this study. The ability to distinguish differential, compartmentalized effects for agonists of estrogen action in the uterus will allow a better risk assessment for new pharmaceuticals that are used as breast cancer chemotherapeutic agents, especially where their use may also be associated with an increased risk of uterine cancers, in particular.

Animals↗

PubMed1999

Effects of in-season (5 weeks) creatine and pyruvate supplementation on anaerobic performance and body composition in American football players.

The purpose of this investigation was to study the efficacy of two dietary supplements on measures of body mass, body composition, and performance in 42 American football players. Group CM (n = 9) received creatine monohydrate, Group P (n = 11) received calcium pyruvate, Group COM (n = 11) received a combination of calcium pyruvate (60%) and creatine (40%), and Group PL received a placebo. Tests were performed before (T1) and after (T2) the 50 week supplementation period, during which the subjects continued their normal training schedules. Compared to P and PL, CM and COM showed significantly greater increases for body mass, lean body mass, 1 repetition maximum (RM) bench press, combined 1 RM squat and bench press, and static vertical jump (SVJ) power output. Peak rate of force development for SVJ was significantly greater for CM compared to P and PL. Creatine and the combination supplement enhanced training adaptations associated with body mass/composition, maximum strength, and SVJ; however, pyruvate supplementation alone was ineffective.

Adolescent↗

PubMed1999

Comparative hazards of chrysotile asbestos and its substitutes: A European perspective.

Although the use of amphibole asbestos (crocidolite and amosite) has been banned in most European countries because of its known effects on the lung and pleura, chrysotile asbestos remains in use in a number of widely used products, notably asbestos cement and friction linings in vehicle brakes and clutches. A ban on chrysotile throughout the European Union for these remaining applications is currently under consideration, but this requires confidence in the safety of substitute materials. The main substitutes for the residual uses of chrysotile are p-aramid, polyvinyl alcohol (PVA), and cellulose fibers, and it is these materials that are evaluated here. Because it critically affects both exposure concentrations and deposition in the lung, diameter is a key determinant of the intrinsic hazard of a fiber; the propensity of a material to release fibers into the air is also important. It is generally accepted that to be pathogenic to the lung or pleura, fibers must be long, thin, and durable; fiber chemistry may also be significant. These basic principles are used in a pragmatic way to form a judgement on the relative safety of the substitute materials, taking into account what is known about their hazardous properties and also the potential for uncontrolled exposures during a lifetime of use (including disposal). We conclude that chrysotile asbestos is intrinsically more hazardous than p-aramid, PVA, or cellulose fibers and that its continued use in asbestos-cement products and friction materials is not justifiable in the face of available technically adequate substitutes.

Air Pollution↗

PubMed1998

Structural requirements for alpha 9 beta 1-mediated adhesion and migration to thrombin-cleaved osteopontin.

Osteopontin is an RGD-containing glycoprotein that mediates adhesion and migration of a variety of different cell types. We recently showed that a recombinant osteopontin fragment that was expected to be formed following thrombin cleavage was not only biologically active, but also could support alpha 9 beta 1-mediated adhesion, an activity not found in the full-length molecule. In this study we defined binding sites on the N-terminal osteopontin fragment important for alpha 9 beta 1-mediated cell interactions. In addition to adhesion, we showed that alpha 9 beta 1 could mediate cell migration, a function not previously identified for this integrin. Using site-directed mutagenesis, we made specific mutations in the RGD region of the N-terminal osteopontin fragment. Mutation of RGD to RGE resulted in a 50% decrease in cell adhesion. The residual binding to the RGE mutant could be blocked by alpha 9 and beta 1 antibodies. Adhesion to the RGE mutant was due to residual recognition of the RGE site by alpha 9 beta 1 since mutants containing more drastic mutations in the RGD domain achieved by mutating RGD to RAA or by eliminating the RGD completely failed to support cell adhesion and migration. In contrast, alpha 9 beta 1-mediated adhesion to tenascin was RGD independent. These data demonstrate that alpha 9 beta 1 is one of the few integrin receptors that can interact with two distinct RGD-containing ligands through different adhesive domains.

Binding Sites↗

PubMed1998

The effect of a low-protein diet and dietary supplementation of threonine on tyrosine and 2-(2-nitro-4-trifluoromethylbenzoyl) cyclohexane-1,3-dione-induced corneal lesions, the extent of tyrosinemia, and the activity of enzymes involved in tyrosine catabolism in the rat.

Rats fed a low-protein diet and administered 2-(2-nitro-4-trifluoromethylbenzoyl)cyclohexane-1,3-dione (NTBC) orally at 30 mumol/kg/day (10 mg/kg/day) or fed a low-protein diet containing 5 ppm NTBC develop lesions to the cornea of the eye within 3-8 days of exposure with an incidence of about 80%. This treatment also produces a marked inhibition of both hepatic and renal 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity, an induction of hepatic but not renal tyrosine amino transferase activity, and a marked tyrosinemia in the plasma and aqueous humor. The extent of tyrosinemia and changes in the activity of tyrosine catabolic enzymes are similar to those reported for rats fed a normal protein diet and administered NTBC orally at 30 mumol/kg/day. However, the onset of corneal lesions occurs much earlier in rats fed a low-protein diet. The adverse ocular effects of NTBC can be alleviated by supplementing the low-protein diet with 1% w/w threonine. The protection afforded by threonine inclusion in the diet was not due to any amelioration in the extent of inhibition of hepatic HPPD activity or reduction in the extent of the tyrosinemia as measured 8 days after treatment. Rats fed L-tyrosine at 5% w/w in a low-protein diet rapidly develop lesions to the cornea of the eye, which are associated with a marked tyrosinemia, increased hepatic tyrosine aminotransferase activity, and about a 50% reduction in the activity of hepatic HPPD. The onset of corneal lesions produced by feeding a high tyrosine diet could be delayed, but not prevented, by inclusion of 1% w/w threonine in the low-protein diet. The basis for the beneficial effect of dietary supplementation of threonine in alleviating the corneal lesions produced by NTBC is unclear. However, our findings do illustrate that protein deficiency limits the ability of the rat to respond to a tyrosine load produced by inhibition of HPPD.

4-Hydroxyphenylpyruvate Dioxygenase↗

PubMed1998

Determination of DNA damage in F344 rats induced by geometric isomers of tamoxifen and analogues.

To investigate the activation mechanisms involved in tamoxifen carcinogenicity, analogues of tamoxifen isomers modified at the ethyl group were synthesized and assessed for their ability to induce hepatic DNA damage following their administration to female F344 rats. The cis isomer was prepared by acid-catalyzed isomerization of tamoxifen and isolated by preparative HPLC. The active metabolite alpha-hydroxytamoxifen and geometric isomers of bromotamoxifen and C-desmethylenetamoxifen, analogues in which the ethyl group has been replaced by a bromine atom and methyl group, respectively, were synthesized according to published procedures. The levels of hepatic DNA adducts induced were determined by 32P-postlabeling. Bromotamoxifen and tamoxifen 1,2-epoxide caused no detectable DNA damage relative to controls. Trans isomers of tamoxifen, C-desmethylenetamoxifen, and alpha-hydroxytamoxifen all produced DNA adducts at a 5-90-fold higher level than the corresponding cis isomers. In contrast, both the cis and trans isomers of alpha-hydroxytamoxifen showed similar reactivity toward calf thymus DNA in vitro. Molecular models of alpha-hydroxytamoxifen isomers suggest this difference in DNA adduct-forming ability is due to steric hindrance of the enzymes involved in the activation of this metabolite. There were high adduct levels in the liver, but no uterine DNA adducts were detected in rats treated with alpha-hydroxytamoxifen. This suggests that in contrast to the liver, alpha-hydroxytamoxifen is not further activated in rat uterus. This may help to explain the absence of uterine tumors in rats following long-term tamoxifen treatment.

Animals↗

PubMed1998

From toxicological problem to therapeutic use: the discovery of the mode of action of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), its toxicology and development as a drug.

NTBC is a triketone with herbicidal activity that has been shown to have a novel mode of action by inhibiting the enzyme 4-hydroxyphenylpyruvate dioxygenase in plants. Early studies on the toxicity of this compound found that rats treated with NTBC developed corneal lesions. Investigations aimed at understanding the mechanistic basis for the ocular toxicity discovered that the rats developed tyrosinaemia and excreted large amounts of 4-hydroxyphenylpyruvate and 4-hydroxyphenyllactate, owing to inhibition of the hepatic enzyme 4-hydroxyphenylpyruvate dioxygenase. The corneal lesions resemble those seen when rats are fed a diet supplemented with tyrosine, leading us to conclude that the ocular toxicity seen with NTBC is a consequence of a marked and sustained tyrosinaemia. Studies in collaboration with Professor Sven Lindstedt showed that NTBC was a potent inhibitor of purified human liver 4-hydroxyphenylpyruvate dioxygenase. This interaction lead to the concept of using NTBC to treat patients with tyrosinaemia type 1, to block or reduce the formation of toxic metabolites such as succinylacetoacetate in the liver. Zeneca Agrochemicals and Zeneca Pharmaceuticals made NTBC available for clinical use and, with the approval of the Swedish Medical Products Agency, a seriously ill child with an acute form of tyrosinaemia type 1 was successfully treated in February 1991. Subsequently, other children with this inborn error of metabolism in Sweden and other countries have been treated with NTBC. The drug is now available to those in need via Swedish Orphan AB.

4-Hydroxyphenylpyruvate Dioxygenase↗