Comparison of bone-implant interface shear strength of hydroxyapatite-coated and alumina-coated metal implants

We performed a transcortical push-out test to determine the effect of surface roughness of hydroxyapatite (HA)-coated implants on bone-implant shear strength in a canine model. Hydroxyapatite- and alumina-coated SUS316L with the same surface roughness (roughness average: Ra = 5 microns) and HA-coated Ti-6A1-4V (Ra = 8.4 microns), sintered HA (Ra = 0.9 micron), and dense alumina (Ra = 1.3 microns) were inserted into the dog's femur. The interface shear strength of the dense alumina was significantly lower than that of other implants at both 4 and 12 weeks after implantation. At 4 weeks after implantation, the interface shear strength of the alumina-coated SUS316L was significantly lower than that of other implants (P < .05) except the dense alumina, but at 12 weeks, there was no significant difference between the implant types except the dense alumina. This indicates that the surface roughness of the HA coating affects the enhancement of the bone-implant interface shear strength at the early period after implantation, and that a surface roughness of several micrometers does not influence the bond strength between bone and HA. A scanning electron microscopic study indicated that in almost all cases at 12 weeks, the failure site after push-out testing was the coating-substrate interface, not the coating-bone interface. Therefore, protection of the coating-substrate interface from direct shear loading is needed.

Reassessment of the two-site enzyme immunoassay for human epidermal growth factor (hEGF) and measurement of immunoreactive hEGF in human sera and urine

We reassessed the enzyme immunoassay (EIA) system for hEGF previously developed by our laboratory (Clin Chim Acta 156:51-60, 1985), since it appeared that the reported EIA system detected not only hEGF but also pS2 protein owing to minor contamination by pS2 protein in the hEGF sample used for immunization. In this study, we purified the hEGF sample using Benzamidine-Sepharose 6B column chromatography as a critical step for purification and newly developed an EIA system with specificity for hEGF. We also measured the hEGF level in serum, plasma, and urine from normal subjects by our new EIA system and found that the values measured by the previous system were 1.2-5.8-fold higher than the new system values. These results suggest that the previous system detected "hEGF" in excess owing to the nonspecificity of the antibody used. We investigated the molecular nature of immunoreactive hEGF detected in serum using our new system and confirmed that considerable amounts of immunoreactive hEGF exist as a high molecular weight form through S-S linkage with some macromolecule(s) in human blood as reported previously (Biochem Int 12:677-683, 1986).

Cloning and characterization of a c-myc intron binding protein (MIBP1)

The cDNA for a c-myc intron 1 binding protein 1 (MIBP1) in the rat was isolated from lambda gt11 and lambda ZAPII cDNA libraries. Sequencing of the cDNA clones revealed a long ORF which encoded a putative protein of 2437 amino acid residues. This protein has two widely separated zinc finger regions, each of which carries C2H2 motifs. When expressed in E. coli as a fusion protein, part of the MIBP1 showed sequence-specific binding to the target sequence, i.e., a 9-bp sequence in the rat c-myc intron 1. MIBP1 is most likely the rat counterpart of human MHC binding protein-2 (MBP-2/HIV-EP2), based on the 86% similarity in nucleotide sequence and 93% similarity in amno acid sequence. Northern blotting revealed a high level of MIBP1 mRNA in the brain.

Survey of complications of indocyanine green angiography in Japan

PURPOSE

We evaluated the safety of indocyanine green for use in fundus angiography.

METHODS

We sent a questionnaire concerning complications of indocyanine green to 32 institutions in Japan, which were selected on the basis of the client list from the Topcon Company, which manufactures the indocyanine green fundus camera.

RESULTS

Ophthalmologists at 15 institutions responded, reporting a total of 3,774 indocyanine green angiograms performed on 2,820 patients between June 1984 and September 1992. Before angiography, intradermal or intravenous indocyanine green testing, or both was performed at 13 of 15 institutions. For three patients, the decision was made not to proceed with angiography after positive preangiographic testing. The dosage of indocyanine green used for angiography varied from 25 to 75 mg, depending upon the institution. There were 13 cases of adverse reactions (0.34%), ten of which were mild reactions such as nausea, exanthema, urtication, itchiness, and urgency to defecate, and did not require treatment. Also recorded were one case of pain of the vein, which required treatment, and two cases of hypotension. The two hypotensive patients required treatment for shock.

CONCLUSIONS

A comparison of frequency of adverse reactions to indocyanine green with the previously reported frequency of such reactions to fluorescein sodium indicated that indocyanine green is a safe as fluorescein for use in angiography.

[Low-dose continuous infusion therapy 5-FU and CDDP enabled terminal patients with lung and rectal cancer to remain at home]

CDDP and 5-FU are time dependent drugs and their increasing effect is expected because of the dual chemical modulation. The low dose continuous infusion of CDDP and 5-FU was applied to the terminal adenocarcinoma patients with the metastatic lesions. One patient was 42 years old lung cancer patient with the metastatic lesions in the liver, the bone, the pericardial space, the underskin, the muscles and the lymph nodes (stage IV). The another patient was 61 years old rectum cancer patient with lung and hepatic metastasis (stage V). Both patients were directly informed of the true name of the disease and the poor curability from the physician in charge. The physician promised them to take the home therapy as much as possible in order to pursuit their own life value at home. The lung cancer patient got the radiotherapy first to remove the bone pain and the rectum cancer patient was operated to make the stoma to avoid the obstructive ileus beforehand. After the therapy, two patients took the low dose continuous infusion of CDDP and 5-FU. In both cases, the abdominal symptoms such as nausea and vomiting due to the therapy were not recognized and the hematopoietic disorders and the renal failure were slight, so they could get the therapy continuously for very long. The lung cancer patient lived 9 months after the diagnosis and the low dose infusion chemotherapy has continued for 7 months, the home stay for 4 months. The rectum cancer patient lived 13 months and the same chemotherapy has continued for 12.5 months, the home stay for 7.5 months. The low dose continuous infusion therapy of CDDP and 5-FU is an effective treatment for terminal cancer patients as one of the home therapies from the point of the QOL (quality of life).

Adsorption of salivary proteins to the surface of oral streptococcal cells

Oral tissues, especially tooth surfaces, are covered with a layer of salivary proteins. Oral bacterial cells that adsorb to salivary components accumulated on the tooth surface are, as a rule, covered with the same components, especially proteins. Thus, it is possible that the salivary proteins covering the bacterial cells are related to the adhesion of bacteria to oral tissues. The aim of this study was to clarify the mechanisms of adsorption of salivary proteins to the surface of Streptococcus sanguis, S. mitis and S. salivarius using an adsorption assay with salivary proteins labeled with tritiated formaldehyde. The results showed that salivary proteins adsorbed more to S. salivarius than to S. mitis, and least to S. sanguis. It was evident that hydrophobic bonding was involved in the adsorption of salivary proteins to the bacterial cells tested. The amount of salivary proteins adsorbed to S. mitis and S. salivarius was decreased by the presence of phosphate, that to S. sanguis was increased by the presence of a divalent cation such as Ca2+, and that to all bacteria tested was inhibited in different ways by the presence of sugars. The amount of salivary proteins adsorbed to S. sanguis and S. salivarius was reduced effectively by pretreatment of the cells with trypsin, chymotrypsin and papain. In the case of S. mitis, the amount of adsorbed salivary proteins was decreased by pretreatment of the cells with chymotrypsin only, and was increased by pretreatment with lipase. These results indicate that there are different mechanisms of adsorption of salivary protein to the cell surfaces of oral streptococci.

Effects of dietary corticosterone and trilostane on growth and skeletal muscle protein turnover in broiler cockerels

1. The effects of dietary corticosterone and trilostane, an inhibitor of glucocorticoid synthesis, on: growth, rates of synthesis and breakdown of skeletal muscle protein, and content of abdominal fat were studied in broiler chickens. 2. Dietary corticosterone (5, 10 or 20 mg/kg) depressed body weight gain and increased abdominal fat content in a dose-dependent manner while dietary trilostane (1.4 or 7.0 mg/kg) had no effect. 3. The rate of protein breakdown in skeletal muscle estimated from N tau-methylhistidine excretion was increased in a dose-dependent manner by dietary corticosterone but it was decreased by trilostane. 4. The rate of skeletal muscle protein synthesis was not affected by corticosterone although it was decreased by trilostane. 5. Plasma corticosterone concentration was increased in a dose-dependent manner by dietary corticosterone and decreased by treatment with 7 mg trilostane/kg diet. 6. The results indicate that higher concentrations of plasma corticosterone increase protein breakdown in skeletal muscle but do not affect muscle protein synthesis while both the rates of synthesis and breakdown are decreased when plasma corticosterone concentration is reduced.

FR901451, a novel inhibitor of human leukocyte elastase from Flexibacter sp. I. Producing organism, fermentation, isolation, physico-chemical and biological properties

A novel human leukocyte elastase (HLE) inhibitor, FR901451 was discovered in the fermentation broth of a bacteria. The bacteria was identified as Flexibacter sp. No. 758. FR901451 has a molecular weight of 1269 and a molecular formula of C60H79N13O18. The mode of inhibition against HLE is competitive, with a Ki value of 9.8 x 10(-9) M.

Case report: the "aurora sign"--a new sonographic sign of pneumatosis cystoides intestinalis

Pneumatosis cystoides intestinalis (PCI) is a rare condition characterized by multiple gas-filled cysts of varying size within the intestinal wall. Although the characteristic findings on plain abdominal radiograph, computed tomography (CT), and barium enema have been well described, the sonographic findings have not. We recently encountered a case of PCI in which abdominal sonography disclosed a unique finding. We were able to reproduce the finding experimentally and have coined it the "aurora sign".

Agarose-carrageenan hybrid polysaccharides from Lomentaria catenata

Two polysaccharide fractions, PS1 and PS2 from Lomentaria catenata consisted of D-Gal, L-Gal, D-Glc, D-Xyl, D-GlcA and sulphate. Partial hydrolysis led to the isolation and identification of oligosaccharides indicating the co-existence of an agarose and carrageenan backbone structure, in which D-Glc and D-GlcA residues occur as single units branching at O-3 of -->4)alpha-D-Gal(1--> and O-4 of -->3)beta-D-Gal(1-->, respectively.

[A case of Jordans' anomaly]

A 35-years old female with Jordans' anomaly was reported. She had been treated for diabetes mellitus and hypertension at another hospital. She was admitted to our hospital for operation for diabetic retinopathy on July 9, 1992. Wright-Giemsa stained peripheral blood smear revealed multiple vacuoles in the cytoplasm of the granulocytes and monocytes. Histochemical studies of these vacuoles showed positive for Sudan III but negative for peroxidase, alkaline phosphatase and PAS staining. Electron microscopic examination revealed that lipid containing vacuoles had no clear membrane and were not associated with cell organelles. Laboratory findings of the serum showed hyperglycemia (FBS 188mg/dl), high HbA1c level (9.4%) and mild type IIa hyperlipidemia. Abdominal sonogram and abdominal CT showed no remarkable abnormalities except for mild fatty liver. Her elder sister and daughter had similar morphological findings in granulocytes, monocytes and lymphocytes.

Renal protective effect of efonidipine hydrochloride (NZ-105), a new calcium antagonist, in spontaneously hypertensive rats

1. We investigated the renal protective effect of efonidipine hydrochloride (NZ-105) in spontaneously hypertensive rats (SHR). SHR were given a diet containing 0.075% NZ-105 from 8 weeks old for 20 weeks. 2. 24-hr urinary protein excretion in the control SHR (drug-free diet) increased with age (from 77.3 mg/kg/day at 8 weeks old to 385.4 mg/kg/day at 28 weeks old), while that in NZ-105-treated SHR was maintained at almost the same level as that in Wistar-Kyoto rats (WKY), matched control animals throughout the experimental period. 3. The histological changes of the kidney were examined by light microscopy at the end of the treatment period. In control SHR, swelling and hyalinization of glomeruli, dilatation of renal tubules containing hyaline casts and arteriolosclerosis were revealed. The long-term administration of NZ-105 markedly suppressed these changes. 4. The kidney weights and plasma creatinine concentration in control SHR were higher than those in WKY, while they were significantly reduced in NZ-105-treated SHR. The long-term administration of NZ-105 also suppressed the elevation of systolic blood pressure and the increases of plasma renin activity and aldosterone concentration. 5. These findings suggest that NZ-105 inhibits the development of proteinuria and progressive kidney damage in SHR and may become a useful antihypertensive drug with the renal protective effect.

Effect of pravastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, on hepatic cholesterol 7 alpha-hydroxylase, acyl-coenzyme A: cholesterol acyltransferase, and bile lipid secretion in the hamster with intact enterohepatic circulation

The effects of administration of pravastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on hepatic cholesterol 7 alpha-hydroxylase and acyl-coenzyme A: cholesterol acyltransferase (ACAT) activities and bile lipid secretion were investigated in Syrian golden hamsters. Continuous administration of pravastatin induced no significant changes in hepatic cholesterol content, ACAT and cholesterol 7 alpha-hydroxylase activities, or bile lipid and acid composition. Abrupt withdrawal of pravastatin induced increases in hepatic cholesterol content and ACAT activity and no change in hepatic cholesterol 7 alpha-hydroxylase activity, and increased cholesterol saturation in bile. Hepatic cholesterol 7 alpha-hydroxylase activity paralleled hepatic mRNA levels of this enzyme. These results suggest that a change in hepatic cholesterol metabolism induced by continuous administration of pravastatin maintains a constant net balance of hepatic cholesterol content. In addition, the drug has no deleterious influence on metabolism of bile lipids and acids and related enzymes, except for a transient increase in cholesterol saturation in bile induced by an inappropriate increase in hepatic cholesterol content and a lack of response of cholesterol 7 alpha-hydroxylase activity to changes in hepatic cholesterol content upon abrupt withdrawal of pravastatin.

Multiple intrahepatic aneurysms following transcatheter arterial embolization. Work in progress

PURPOSE

To discuss the mechanism of multiple intrahepatic aneurysm formation after transcatheter arterial embolization (TAE) performed in five patients with hepatocellular carcinoma.

MATERIALS AND METHODS

TAE was performed with gelatin sponge particles and iodized oil as embolic materials. Mitomycin C was also used in four cases.

RESULTS

Three to 14 aneurysms 1-6 mm in diameter were found in third-to sixth-order branches of the hepatic arteries at repeat angiography performed 25-45 days after TAE. Follow-up angiograms in three cases revealed that most aneurysms were no longer apparent except in one patient in whom two aneurysms remained and were larger than before. In none of the five cases were any signs of aneurysm rupture noted.

CONCLUSION

Radiologists should be aware of this complication of TAE. It is speculated that the main cause of aneurysm formation in these patients was the embolic agents used.

Interaction of marine toxin dolastatin 10 with porcine brain tubulin: competitive inhibition of rhizoxin and phomopsin A binding

Dolastatin 10, a cytostatic peptide containing several unique amino acid subunits, was isolated from the marine shell-less mollusk Dolabella auricularia. It inhibits microtubule assembly at concentrations below 5.0 microM (IC50, 3.0 microM) and causes formation of tubulin aggregates at higher (> 10 microM) concentrations in a somewhat different manner from that caused by vinblastine. Electron microscopical analysis showed irregular aggregates of microtubule proteins in the presence of 10 microM dolastatin 10. Dolastatin 10 inhibited the binding of both radiolabeled rhizoxin and phomopsin A to tubulin with inhibition constants (Ki) of 7 x 10(-8) M and 1 x 10(-7) M, respectively. The results suggest that at least one of the binding sites of dolastatin 10 on tubulin is the rhizoxin binding site.

Identification of disulfide bridges in a cardiotoxic peptide by electrospray ionization

A new method was developed for subjecting a peptide to a specified number of Edman degradation cycles on an automated polypeptide sequencer and desorbing the residual peptide for further investigations. The procedure was applied in combination with electrospray ionization mass spectrometry to identify the four disulfide bridges present in a small tightly bound peptide. The task was accomplished using only a few nanomoles of the intact peptide.

Dual energy X-ray absorptiometry of the calcaneus: comparison with other techniques to assess bone density and value in predicting risk of spine fracture

OBJECTIVE

The calcaneus has been proposed as an alternative site for assessment of bone mineral density (BMD) in women with osteoporosis. The objectives of this study were to evaluate the clinical usefulness of dual-energy X-ray absorptiometry (DXA) of the calcaneus for predicting spinal fracture and to compare the predictive value of assessment of BMD by DXA of the calcaneus, quantitative CT or DXA of the lumbar spine, and DXA of the most distal part of the radius.

SUBJECTS AND METHODS

The study group consisted of 399 healthy volunteer women (aged 19-81 years) and 27 women (aged 44-85 years) who had osteoporosis. They had DXA of the calcaneus, quantitative CT and DXA of the lumbar spine, and DXA of the most distal part of the radius. T-score analyses were used to compare decreases in BMD in postmenopausal women with decreases in premenopausal women, and to compare decreases in women with and without osteoporosis.

RESULTS

T-score analysis of age-related changes in BMD in the control subjects showed that densities in the calcaneus, the lumbar spine, and the most distal part of the radius decrease significantly with age in postmenopausal women. In women with osteoporosis (n = 27), BMDs in the calcaneus (DXA, p < .0002), L1-L3 (quantitative CT, p < .0001), L1-L4 (DXA, p < .0005), and the most distal part of the radius (DXA, p < .005) were significantly lower than those in healthy control subjects (n = 77). T-score analysis indicated that in women with osteoporosis, DXA of the calcaneus showed BMD losses greater than those shown by DXA of L1-L4 and the most distal part of the radius and similar to those shown by quantitative CT of L1-L3. Receiver-operating characteristic (ROC) analysis showed that findings on DXA of the calcaneus were as good a predictor of the risk of spinal fracture as findings on DXA of the lumbar spine and not as good as findings on quantitative CT of the lumbar spine.

CONCLUSION

The results suggest that DXA assessment of BMD in the calcaneus is not a useful adjunct to other measurements. However, it can be used to predict the risk of fracture when better measures, such as quantitative CT, are unavailable.

Drebrin, a development-associated brain protein from rat embryo, causes the dissociation of tropomyosin from actin filaments

Drebrin is a development-associated neuroprotein whose cDNA into fibroblasts causes the formation of dendrite-like structures (Shirao, T., Kojima, N., and Obata, K. (1992) Neuroreport 3, 109-112). To explore molecular functions of drebrin during brain development, we purified drebrin from brains of rat embryos. Drebrin bound to actin filaments at a stoichiometry of 1:5 with a dissociation constant (Kd) of 1.2 x 10(-7) M. It strongly inhibited the actin binding activity of tropomyosin. Excess amounts of tropomyosin also inhibited the drebrin binding to actin filaments, suggesting that drebrin and tropomyosin competitively bind to actin filaments. Further, drebrin inhibited not only the actin binding activity of alpha-actinin but also the actin cross-linking activity of alpha-actinin. Gene transfection experiments revealed that tropomyosin was dissociated from actin filaments in drebrin-overexpressing fibroblasts. Thus we hypothesize that drebrin may destabilize actin filaments by dissociating tropomyosin and alpha-actinin from actin filaments, resulting in the formation of axon and dendrites during neuronal development.

The two subunits of a phospholipase A2 inhibitor from the plasma of Thailand cobra having structural similarity to urokinase-type plasminogen activator receptor and LY-6 related proteins

Amino acid sequences of the two subunits (31-kDa and 25-kDa subunits) of a phospholipase A2 (PLA2) inhibitory protein, purified from the blood plasma of Thailand cobra Naja naja kaouthia, were determined by alignment of peptides obtained by lysyl endopeptidase, staphylococcal V8 protease and endoproteinase Asp-N digestions. The respective subunits were composed of 188 and 185 amino acid residues, and the former contained one asparagine-linked sugar chain at the position 157. There was 29% identity between 31-kDa and 25-kDa subunits. The analysis of internal homology in each sequence of the two subunits revealed the existence of two repeats of approximately 90 amino acid residues. These sequence units were found to be significantly homologous to those of urokinase-type plasminogen activator receptor and of Ly-6 related proteins, such as Ly-6A/E, Ly-6C, ThB, and CD59 antigens.

Epidemiologic study of Chlamydia trachomatis infection in pregnant women

GOAL OF THE STUDY

The presence of Chlamydia trachomatis in the cervical canal was investigated in 10,980 married pregnant women and 1,792 unmarried pregnant women who underwent artificial abortions in Hokkaido.

STUDY DESIGN

Cervical canal smears were screened for C. trachomatis in pregnant patients.

RESULTS

In the married women, the detection rate of C. trachomatis was 5.6% (615 of 10,980 cases). In the unmarried women, the detection rate of C. trachomatis was 15.2% (272 of 1,792 cases). Stratification of the data on the detection of C. trachomatis as a function of the subjects' age showed that, for both the married and the unmarried women, the detection rate increased as the age of the subjects decreased. Analysis of the detection rate of C. trachomatis as a function of the year revealed that it had not changed since 1986.

CONCLUSIONS

The findings in this study show that there has been an epidemic of asymptomatic C. trachomatis infections in Hokkaido, especially in young women.

Inhibition of serine proteases of the blood coagulation system by squash family protease inhibitors

Squash family inhibitors are the smallest protein serine protease inhibitors, being composed of approximately 30 amino acid residues. We isolated 8 squash family inhibitors from the seeds of bitter gourd, squash, gourd and luffa and examined their effect on serine proteases of the blood coagulation system. Five of them prolonged the activated partial thromboplastin time of human plasma to various extents, but three did not. Only Momordica charantia (bitter gourd) trypsin inhibitor-II prolonged the prothrombin time of human plasma. All inhibitors inhibited the amidolytic activities of factor XIIa, plasma kallikrein, factor Xa, but did not inhibit significantly those of factor XIa, factor IXa, factor VIIa, and thrombin. Ki values for factor XIIa, plasma kallikrein, and factor Xa were in the order of 10(-6)-10(-9), 10(-4)-10(-5), and 10(-4)-10(-6)M, respectively. The prolongation of the activated partial thromboplastin time by inhibitors appeared to correspond to their inhibitory potencies for factor XIIa. Momordica charantia trypsin inhibitor-II, which has the strongest inhibitory potency toward the amidolytic activity of factor Xa, with a Ki value 10-100 times smaller than those of other inhibitors, inhibited the activation of factor X by factor VIIa-tissue factor complex or factor IXa, while others did not.

A case of neural cell adhesion molecule-positive peripheral T-cell lymphoma associated with human T-cell lymphotrophic virus type 1 showing an unusual involvement of the gastrointestinal tract during the course of the disease

We report a case of neural cell adhesion molecule (NCAM)-positive peripheral T-cell lymphoma (PTCL), pleomorphic, medium and large cell type according to the updated Kiel classification, which was associated with human T-cell lymphotrophic virus type 1 (HTLV-1). The patient showed an unusual involvement of the gastrointestinal tract forming a bulky mass during the course of his disease, and a relatively indolent clinical course for 53 months until death. Phenotypic analysis showed CD2+, CD3-, CD4+, CD5+, CD7+, CD8-, CD16-, CD56+, and CD57- phenotype. Human T-cell lymphotrophic virus type 1 antibody was detected by the enzyme-linked immunosorbent assay. The proviral integration of HTLV-1 and the monoclonal rearrangements of T-cell receptor beta and gamma genes also were confirmed in DNA extract from fresh material. This fact calls attention to NCAM as one of the potential factors playing a role in the localization and behavior of lymphomas even within the category of PTCL associated with HTLV-1, ie, adult T-cell leukemia/lymphoma (ATLL).

Effect of basic fibroblast growth factor on synthesis/secretion of pS2 protein by human breast cancer cells (MCF-7)

pS2 is an estrogen-induced mRNA species that was originally identified in the breast cancer cell line MCF-7. Exposure of the cells to basic fibroblast growth factor (bFGF) at the concentration of 10-100 ng/ml for 48-72 h resulted in a marked increase in the concentration of pS2 protein in the medium. The polymerase chain reaction with reverse transcriptase revealed that bFGF increased the amount of intracellular pS2 mRNA: immunocytochemical studies showed that exposure to the factor increased the amount of intracellular pS2 protein. Simultaneous addition of cycloheximide with bFGF completely abolished induction of pS2 protein, although it did not affect the induction of pS2 mRNA. Actinomycin D did not affect the stimulatory effect of bFGF on synthesis/secretion of pS2 protein. bFGF effectively abolished decay of the pS2 mRNA level caused by actinomycin D. These results suggest that the induction of the synthesis/secretion of pS2 protein by bFGF occurs at the post-transcriptional level, most probably due to the stabilization of pS2 mRNA. Another finding, that bFGF and estradiol have a synergistic effect on induction of pS2 protein, suggests the possibility that these two inducers act by a different but partly overlapping mechanism.