Design, synthesis and characterization of linear unnatural amino acids for skin moisturization.

OBJECTIVES: This work aimed to design, synthesize and characterize replacement natural moisturizing factor (NMF) composed of modified hygroscopic linear amino acids to pre-empt or repair skin barrier dysfunction. METHODS: Following synthesis and characterization, thermo-gravimetric analysis and quantum mechanics molecular modelling quantified and depicted water binding to the new compounds. Deliquescence relative humidity demonstrated the water-scavenging ability of the compounds, whereas snake skin moisturizing studies showed they increased water uptake into snake skin. RESULTS: From thermal analysis, N-hydroxyglycine showed greatest water-holding capacity followed by N-hydroxyserine, l-homoserine and α-hydroxyglycine; coupled with quantum mechanics molecular modelling, between 8 and 12 molecules of water could associate with each molecule of either N-hydroxyglycine, N-hydroxyserine or l-homoserine. All of our modified amino acids were efficacious and induced similar or greater water uptake compared with the established moisturizing compounds hyaluronic acid, glycerine and urea in snake skin. Incorporated at 10% in Oilatum, N-hydroxyserine induced >200% greater moisture uptake into dry snake skin compared to treatment with water alone, with efficacy related to the molecule structure and ability to bind to 12 water molecules. Oilatum cream spiked with all our unnatural amino acid hydrotropes increased water uptake into snake skin compared with Oilatum alone. The compound series was designed to elucidate some structure - efficacy relationships. Amino acid chirality did not affect the water-holding capacity but did affect uptake into skin. Compounds with high melting points and bond energies tended to decrease water-holding capacity. With isosteric replacement, the more electronegative atoms gave greater water-holding capacities. CONCLUSIONS: This work demonstrates the potential of unnatural amino acid hydrotropes as skin moisturizers and has developed some predictive 'rules' for further design and refinement of chemical structures.

Systemic oxygen extraction during exercise at high altitude.

BACKGROUND: Classic teaching suggests that diminished availability of oxygen leads to increased tissue oxygen extraction yet evidence to support this notion in the context of hypoxaemia, as opposed to anaemia or cardiac failure, is limited. METHODS: At 75 m above sea level, and after 7-8 days of acclimatization to 4559 m, systemic oxygen extraction [C(a-v)O2] was calculated in five participants at rest and at peak exercise. Absolute [C(a-v)O2] was calculated by subtracting central venous oxygen content (CcvO2) from arterial oxygen content [Formula: see text] in blood sampled from central venous and peripheral arterial catheters, respectively. Oxygen uptake [Formula: see text] was determined from expired gas analysis during exercise. RESULTS: Ascent to altitude resulted in significant hypoxaemia; median (range) [Formula: see text] 87.1 (82.5-90.7)% and [Formula: see text] 6.6 (5.7-6.8) kPa. While absolute C(a-v)O2 was reduced at maximum exercise at 4559 m [83.9 (67.5-120.9) ml litre(-1) vs 99.6 (88.0-151.3) ml litre(-1) at 75 m, P=0.043], there was no change in oxygen extraction ratio (OER) [C(a-v)O2/CaO2] between the two altitudes [0.52 (0.48-0.71) at 4559 m and 0.53 (0.49-0.73) at 75 m, P=0.500]. Comparison of C(a-v)O2 at peak [Formula: see text] at 4559 m and the equivalent [Formula: see text] at sea level for each participant also revealed no significant difference [83.9 (67.5-120.9) ml litre(1) vs 81.2 (73.0-120.7) ml litre(-1), respectively, P=0.225]. CONCLUSION: In acclimatized individuals at 4559 m, there was a decline in maximum absolute C(a-v)O2 during exercise but no alteration in OER calculated using central venous oxygen measurements. This suggests that oxygen extraction may have become limited after exposure to 7-8 days of hypoxaemia.

Structural outcomes in the Cleft Care UK study. Part 2: dento-facial outcomes.

OBJECTIVES: To compare facial appearance and dento-alveolar relationship outcomes from the CSAG (1998) and CCUK (2013) studies. SETTING AND SAMPLE POPULATION: Five-year-olds born with non-syndromic unilateral cleft lip and palate. Those in the original CSAG were treated in a dispersed model of care with low-volume operators. Those in CCUK were treated in a more centralized, high-volume operator model. MATERIALS AND METHODS: We compared facial appearance using frontal view photographs (252 CCUK, 239 CSAG) and dental relationships using study models (198 CCUK, 223 CSAG). Facial appearance was scored by a panel of six assessors using a standardized and validated outcome tool. Dento-alveolar relationships were scored by two assessors using the 5-Year-Olds' Index. Ordinal regression was used to compare results between surveys. RESULTS: Excellent or good facial appearance was seen in 36.2% of CCUK compared with 31.9% in CSAG. In CCUK, 21.6% were rated as having poor or very poor facial appearance compared with 27.6% in CSAG. The percentage rated as having excellent or good dento-alveolar relationships was 53.0% in CCUK compared with 29.6% in CSAG. In CCUK, 19.2% were rated as having poor or very poor dento-alveolar relationships compared to 36.3% in CSAG. The odds ratios for improved outcome in CCUK compared to CSAG were 1.43 (95% CI 1.03, 1.97) for facial appearance and 2.29 (95% CI 1.47, 3.55) for dento-alveolar relationships. CONCLUSIONS: Facial and dento-alveolar outcomes were better in CCUK children compared to those in CSAG.

Tropical Peatland Hydrology Simulated With a Global Land Surface Model.

Tropical peatlands are among the most carbon-dense ecosystems on Earth, and their water storage dynamics strongly control these carbon stocks. The hydrological functioning of tropical peatlands differs from that of northern peatlands, which has not yet been accounted for in global land surface models (LSMs). Here, we integrated tropical peat-specific hydrology modules into a global LSM for the first time, by utilizing the peatland-specific model structure adaptation (PEATCLSM) of the NASA Catchment Land Surface Model (CLSM). We developed literature-based parameter sets for natural (PEATCLSMTrop,Nat) and drained (PEATCLSMTrop,Drain) tropical peatlands. Simulations with PEATCLSMTrop,Nat were compared against those with the default CLSM version and the northern version of PEATCLSM (PEATCLSMNorth,Nat) with tropical vegetation input. All simulations were forced with global meteorological reanalysis input data for the major tropical peatland regions in Central and South America, the Congo Basin, and Southeast Asia. The evaluation against a unique and extensive data set of in situ water level and eddy covariance-derived evapotranspiration showed an overall improvement in bias and correlation compared to the default CLSM version. Over Southeast Asia, an additional simulation with PEATCLSMTrop,Drain was run to address the large fraction of drained tropical peatlands in this region. PEATCLSMTrop,Drain outperformed CLSM, PEATCLSMNorth,Nat, and PEATCLSMTrop,Nat over drained sites. Despite the overall improvements of PEATCLSMTrop,Nat over CLSM, there are strong differences in performance between the three study regions. We attribute these performance differences to regional differences in accuracy of meteorological forcing data, and differences in peatland hydrologic response that are not yet captured by our model.

Rose-trellis periosteal release in oral mucosal advancement flaps in pigs.

The aims of this study were to find out whether scoring in a rose-trellis pattern improved the stretch of mucoperiosteal flaps more than conventional scoring in the horizontal plane, and to consider its application in the closure of oroantral communications. Sixteen sections of cadaveric porcine buccal mucoperiosteum were removed from the molar region of the maxilla and mandible. A three-sided flap was raised in the subperiosteal plane, excised, and pinned to a cork board with the periosteal side facing upwards. Eight samples were scored in the horizontal plane (control) using lines perpendicular to the line of simulated advancement, and eight in a rose-trellis or criss-cross pattern. Scoring using a rose-trellis pattern yielded a mean increase in stretch of 24.3% (p=0.0003) when compared with the conventional method. Buccal advancement flaps are widely used to close oroantral communications, and scoring of the mucoperiosteum facilitates the stretching of the tissue over the defect. To be successful, defects should be fully closed to prevent contamination, and closure should be tension-free. In this study, scoring in a rose-trellis pattern increased the stretch of the tissue sample more than scoring in the horizontal plane. The rose-trellis technique therefore could aid the effective closure of oroantral communications.

Oculovagal reflex in paediatric orbital floor fractures mimicking head injury.

BACKGROUND: The oculovagal reflex is well described in ophthalmic surgery, but may be caused by any manner of pressure on the globe. Children with orbital blowout fractures present in a different manner from adults. The classic presentation in children is a white eye injury (ie, no subconjunctival haemorrhage) with upgaze diplopia and general malaise. METHODS: A retrospective audit is presented of paediatric and young adult patients referred to the Orbital Service at St George's Hospital who required surgical intervention. RESULTS: One-third of children with orbital blowout fractures are admitted for head injury observations, while the true cause for the symptoms goes unrecognised and uninvestigated. CONCLUSIONS: Orbital blowout fractures in children require more swift intervention than in adults if muscle ischaemia and permanent impairment of the vision is to be avoided. The delay for head injury observation may therefore compromise the surgical outcome.

Probiotic containing Lactobacillus casei, Lactobacillus bulgaricus, and Streptococcus thermophiles (ACTIMEL) for the prevention of Clostridium difficile associated diarrhoea in the elderly with proximal femur fractures.

The incidence of Clostridium difficile associated diarrhoea (CDAD) is greater in elderly patients. Probiotics may have a beneficial effect in the prevention of CDAD. However, their effect in elderly orthopaedic patients has not been previously reported. Between April 2013 and April 2014, 105 patients admitted with femoral neck fractures, and who required 3days of antibiotics for infection of any cause, were prescribed the probiotic ACTIMEL until 3days after the last antibiotic dose. The incidence of CDAD was compared with historical controls (April 2011￢ﾀﾓApril 2012). There was no significant reduction in the incidence of CDAD in patients receiving probiotics (OR: 0.9; 95% CI 0.27￢ﾀﾓ2.91; p=0.8) and therefore we cannot recommend the use of ACTIMEL containing Lactobacillus casei, Lactobacillus bulgaricus, and Streptococcus thermophiles for this purpose in this patient group.

The clinical significance of metal ion release from cobalt-chromium metal-on-metal hip joint arthroplasty.

Metal-on-metal (MOM) bearings offer extremely low wear and the avoidance of polyethylene but generate metallic wear particles. Although their total volume is dramatically smaller than polyethylene debris, these particles are in the nanometre size range and are many times more numerous. Metallic particles are ingested by macrophages or may be disseminated via lymphatics to the reticuloendothelial system. They corrode, and metal ions are present in the circulation and concentrated in erythrocytes. Excretion of metal ions via the kidneys seems to balance their generation in patients with MOM implants. However, highly sensitive detection methods can be used to show that levels of circulating cobalt and chromium ions are several times the normal level. These concentrations are well within the limits identified as dangerous to health in workers exposed to industrial chemicals, and also considerably lower than the levels found to cause cell toxicity in vitro. The local concentrations of particles and metal ions in the synovial tissue may occasionally exceed these limits and cause tissue necrosis. Clinical experience of lysis is rare in association with MOM bearings, as are hypersensitivity reactions and MOM bearings have had an excellent record over four decades and have a favourable benefit to risk ratio. Further reduction in risk will be achieved by improvement of materials, engineering, and accuracy of insertion.

Development rationale for an articular surface replacement: a science-based evolution.

Hip resurfacing has an enduring appeal because of the advantages of bone conservation and maximal joint stability. However, a far from satisfactory experience with earlier resurfacing designs led to its virtual disappearance in the 1980s. The concept was reintroduced in the late 1990s. The current generation of resurfacing devices generally consisted of a large-diameter metal-on-metal articulation, the femoral components being cemented and the acetabular components utilizing various forms of cementless fixation. The encouraging medium-term results, with a follow-up of up to 8 years using the current generation of surface replacement joints, combined with favourable reports related to long-term performance of some metal bearings have led to a rapid increase in the use of such components with these devices. This trend is most marked in younger, more active patients who have expectations of restoration of lifestyle in addition to improved mobility and pain relief and in whom failure with conventional total hip replacement is much higher than previously reported with more sedentary patients. The aim of this paper is, firstly, to highlight a number of areas of improvement and, secondly, to explain how these may be addressed by making modifications to the design of both implants and instrumentation and to the surgical technique. The areas identified for improvement were tissue preservation (thinner components, and reduced steps between sizes), acetabular cup issues (fixation, insertion, and positioning), femoral component issues (design, loading, and cementation), improved bearing surface characteristics, and simplified precise instrumentation with a low-trauma surgical technique.

Identification and Characterization of Russet on Snap Beans Caused by Plectosporium tabacinum.

Russet symptoms of unknown etiology are sporadically observed on snap bean (Phaseolus vulgaris) pods in New York and Maryland. Symptoms can render the whole crop unmarketable, and seem to appear when heavy rainfall occurs around harvest time. In 2000 and 2004, a microorganism not previously encountered was isolated from russet lesions on snap bean pods from commercial fields in Maryland and New York. Typical russet symptoms were produced on snap bean pods of cv. Brio after inoculation with spores of the isolates. Koch's postulates were also fulfilled. The organism was identified as Plectosporium tabacinum (Van Beyma) M.E. Palm, W. Gams & Nirenberg. A continuous 48-h leaf wetness duration at 23 to 27°C was essential for rapid symptom development. Large (11 cm long on average) snap bean pods were more susceptible to disease than smaller (pin) pods in cvs. Brio and Gold Mine. Light mechanical damage to the pods did not enhance infection. Four isolates of P. tabacinum (three from snap bean pods, one from zucchini) were inoculated onto large pods of the snap bean cvs. Brio, Gold Mine, and Hercules. All four isolates induced a russet on the pods, but the severity was significantly lower with the zucchini isolate.

Nesprin-2-dependent ERK1/2 compartmentalisation regulates the DNA damage response in vascular smooth muscle cell ageing.

Prelamin A accumulation and persistent DNA damage response (DDR) are hallmarks of vascular smooth muscle cell (VSMC) ageing and dysfunction. Although prelamin A is proposed to interfere with DNA repair, our understanding of the crosstalk between prelamin A and the repair process remains limited. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) have emerged as key players in the DDR and are known to enhance ataxia telangiectasia-mutated protein (ATM) activity at DNA lesions, and in this study, we identified a novel relationship between prelamin A accumulation and ERK1/2 nuclear compartmentalisation during VSMC ageing. We show both prelamin A accumulation and increased DNA damage occur concomitantly, before VSMC replicative senescence, and induce the localisation of ERK1/2 to promyelocytic leukaemia protein nuclear bodies (PML NBs) at the sites of DNA damage via nesprin-2 and lamin A interactions. Importantly, VSMCs treated with DNA damaging agents also displayed prelamin A accumulation and ERK compartmentalisation at PML NBs, suggesting that prelamin A and nesprin-2 are novel components of the DDR. In support of this, disruption of ERK compartmentalisation at PML NBs, by either depletion of nesprin-2 or lamins A/C, resulted in the loss of ATM from DNA lesions. However, ATM signalling and DNA repair remained intact after lamins A/C depletion, whereas nesprin-2 disruption ablated downstream Chk2 activation and induced genomic instability. We conclude that lamins A/C and PML act as scaffolds to organise DNA-repair foci and compartmentalise nesprin-2/ERK signalling. However, nesprin-2/ERK signalling fidelity, but not their compartmentalisation at PML NBs, is essential for efficient DDR in VSMCs.

Carbon fluxes from an urban tropical grassland.

Turfgrass covers a large fraction of the urbanized landscape, but the carbon exchange of urban lawns is poorly understood. We used eddy covariance and flux chambers in a grassland field manipulative experiment to quantify the carbon mass balance in a Singapore tropical turfgrass. We also assessed how management and variations in environmental factors influenced CO2 respiration. Standing aboveground turfgrass biomass was 80 gC m(-2), with a mean ecosystem respiration of 7.9 ± 1.1 µmol m(-2) s(-1). The contribution of autotrophic respiration was 49-76% of total ecosystem respiration. Both chamber and eddy covariance measurements suggest the system was in approximate carbon balance. While we did not observe a significant relationship between the respiration rates and soil temperature or moisture, daytime fluxes increased during the rainy interval, indicating strong overall moisture sensitivity. Turfgrass biomass is small, but given its abundance across the urban landscape, it significantly influences diurnal CO2 concentrations.

Ligand-receptor dissociation: a potential mechanism for the attenuation of estrogen action in the juvenile rabbit uterus.

Estradiol binding kinetics and receptor activation were investigated using cytosol estrogen receptor from adult rabbit uterine endometrium and from the undifferentiated uteri of 2-week-old rabbits. The cytosol estrogen receptor from juvenile compared to that from adult rabbit uteri was lower (P less than 0.01) in concentration, was associated with reduced (P less than 0.01) titers of serum estradiol, and had a lower affinity for estradiol (Ka = 10(7) M-1). The equilibrium association constant (Ka) for the estrogen receptor from juvenile uteri was reduced by an increase in the dissociation rate constant (kd), as measured by [3H]E2 dissociation from the receptor. Enhanced steroid-receptor dissociation in juvenile uteri was correlated with a reduced rate (P less than 0.01) of receptor activation, as measured by the binding of steroid-receptor complex to DNA-cellulose. Because receptor activation was limited at elevated temperature (30 C), activation studies were performed at low temperature (0 C), and under these optimum conditions, the change in binding kinetics observed in the juvenile was correlated with a reduced rate of receptor activation. Equilibrium binding of [3H]E2 to the estrogen receptor exhibited positive cooperativity, as indicated by Hill coefficients of 3.39 +/- 0.12 and 3.44 +/- 0.11 for juveniles and adults, respectively. The ratio of bound to free steroid was decreased in cytosol from juvenile compared to adult uteri. Collectively, these results support the hypothesis that the increased off rate and decreased activation rate of estrogen receptor in immature rabbit uteri may represent a mechanism for the attenuation of estrogen action before sexual maturation.

Patients' perspectives of the role of care providers in amyotrophic lateral sclerosis.

Interviews with 41 patients with amyotrophic lateral sclerosis regarding their perspectives of the roles of doctor, nurse, and allied health personnel showed that emotional support, information, and access to assistive devices were the primary expectations that they held for each of these professional roles. In addition, physicians were expected to evaluate the progress of the disease, help with immediate problems, and continue research to find a cure. Patients wanted to see a physician at each clinic visit. In being given the diagnosis of amyotrophic lateral sclerosis, patients expected the physician to be straightforward, honest but not premature, sensitive to patients' readiness for information, and to convey some degree of hope. Patients were accurate in their knowledge of the disease, but came to the clinic expecting help in managing the illness.

EFFECT OF IRRADIANCE AND LIGHT QUALITY ON STARCH SYNTHESIS BY ISOLATED CHLOROPLASTS OF CODIUM FRAGILE.

Net starch synthesis by isolated chloroplasts of the intertidal alga Codium fragile (Suringar) Hariot was determined by enzymic hydrolysis (amyloglucosidase/α-amylase) of solubilized chloroplast samples followed by the measurement of the resultant glucose yields by hexokinase/glucose-6-phosphate dehydrogenase-coupled reactions. Net starch synthesis was only observed between 100 and 375 µmol m-2 s-1 (PAR) corresponding to irradiance values which supported saturating or super-saturating rates of photosynthesis. Light filter inactivation of the light-harvesting complex carotenoids siphonoxanthin and siphonein reduced net starch synthesis by 68 %. These findings are discussed in relation to photosynthesis in an intertidal zone environment.

Observations on chloroplast starch content and synthesis in the intertidal marine alga Codium fragile (Suringar) Hariot.

A marked seasonal response was observed in the starch content of chloroplasts of Codium fragile sampled between November 1983 and November 1984. Chloroplast starch uniformly increased throughout the life-cycle of this alga, reaching a maximum in the summer months of approx. 5 mg glucose equivalents/109 plastids when C. fragile was in the reproductive phase. Chloroplast starch content was found to be inversely proportional to the concentration of stromal phosphate, decreasing linearly from 5 to 2 mg glucose equivalents/109 plastids over a range of stromal phosphate values of 0·75-1·5 µmol PO4 /109 plastids. Similarly, the net amount of starch synthesized over 3 h by isolated chloroplasts increased linearly with respect to initial chloroplast starch content. These observations are discussed in relation to the regulation of starch synthesis by variations in the stromal P1 : PGA ratio.

Effect of inorganic phosphate, 3-phosphoglycerate and glucose-6-phosphate on net starch synthesis by isolated chloroplasts of Codium fragile (Suringar) Hariot.

Net starch synthesis isolated chloroplasts of Codium fragile appears to be regulated in a similar manner to that of vascular plants. Exogenous 10 mol m-3 PGA stimulated net starch synthesis at 200 µmol m-2 s -1 (PPFD) by approx. 69%, whilst 10 mol m-3 P1 not only inhibited synthesis but also promoted net starch degradation. However, unlike vascular plant chloroplasts, 10 mol m-3 G6P was found to stimulate net starch synthesis by approx. 52% under the same conditions. This apparent difference in response to exogenous G6P is discussed in relation to the operation of the P1 -G6P translocator in chloroplasts of this species.

Characterization of chromatin binding sites for different forms of uterine progesterone receptor.

We tested hamster uterine progesterone receptor (Rp) forms for binding to different chromatin preparations. Similar forms of chick oviduct Rp were used for comparison. Hamster Rp elutes from DEAE-Sephacel in the two peaks, peak I at 115 mM KCl and peak II at 205 mM KCl. Chick Rp peaks I and II elute at 125 mM and 300 mM KCl, respectively. Both chick and hamster peak I displayed a higher level of binding to SDS-stripped chromatin (DNA) than to crude chromatin or 4 M guanidine hydrochloride (GuHCl)-extracted (nucleoacidic protein, NAP) chromatin while peak II bound 50% better to the NAP chromatin than to crude chromatin or DNA. 10 mM molybdate was used to stabilize Rp and to increase Rp recovery. Molybdate-stabilized hamster Rp elutes from DEAE at the peak II position and like peak II, binds poorly to DNA. Since molybdate prevents receptor activation, DNA-Rp interactions require activated Rp. Because molybdate did not prevent Rp binding to NAP chromatin, we conclude that both activated and unactivated Rp bind well to that matrix. Activated hamster Rp could be extracted from crude chromatin, NAP chromatin and DNA with 200 mM KCl. Unactivated Rp was extracted from NAP only with 6 M GuHCl or NaSCN, whereas KCl, glycerol or pyridoxal 5'-phosphate were not able to remove unactivated Rp from NAP. Various Rp forms did not compete with [3H]ORG 2058-Rp for binding to NAP but BSA did compete. Thus a large portion of Rp binding to NAP may represent nonspecific binding rather than binding to a finite number of Rp acceptor sites. These results suggest that the binding of activated Rp to crude chromatin may represent the actual acceptor sites in target cell nuclei. Since the high level of Rp binding sites in NAP chromatin may be an extraction artifact, the involvement of proposed masking proteins in regulating the availability of acceptor sites should be reconsidered. As an alternative to acceptor site regulation, changes in the Rp molecule itself may be important. Rp isolated from hamster uteri on days 1-4 of the estrous cycle was incubated with crude chromatin, NAP chromatin and DNA. The apparent level of Rp binding to chromatin and NAP chromatin increased 2.5-fold from day 1 to day 4, but Rp binding to DNA remained constant. This suggests that ovarian cycle-dependent changes occur in the unactivated Rp which affect its interactions with chromatin, and these changes disappear when receptor is activated.(ABSTRACT TRUNCATED AT 400 WORDS)

Nephrotoxicity and hepatotoxicity induced by inhaled bromodichloromethane in wild-type and p53-heterozygous mice.

Bromodichloromethane (BDCM) is a common municipal drinking water disinfection by-product, resulting in widespread trace human exposure via ingestion and inhalation. The present studies were designed to define organ-specific, BDCM-induced toxicity in wild type (p53(+/+)) and heterozygous (p53(+/-)) mice on both the FVB/N and C57BL/6 genetic backgrounds. Mice were exposed to BDCM vapor daily for 6 h/day and 7 days/week at concentrations of 0, 1, 10, 30, 100, or 150 ppm for 1 week and at 0, 0.3, 1, 3, 10, or 30 ppm for 3 weeks. In the 1-week exposure study, dose-dependent mortality and morbidity were observed at concentrations of 30 ppm and above and were as high as 100% at 150 ppm. In the 3-week exposure study, mortality and morbidity were found only in the 30-ppm exposure groups and were 0, 17, 67, and 33% for the wild-type C57BL/6, p53(+/-) C57BL/6, wild-type FVB/N, and p53(+/-) FVB/N mice, respectively. BDCM was a particularly potent kidney cytotoxicant. Dose-dependent tubular degeneration, necrosis, and associated regenerative cell proliferation greater than 10-fold over controls were seen at concentrations as low as 10 ppm in the kidneys of all strains at 1 week. Similar dose-dependent increases in hepatic necrosis, degeneration, and regenerative cell proliferation were observed but were induced only at concentrations of 30 ppm and higher. Pathological changes were more severe in the FVB/N compared to the C57BL/6 mice and were more severe in the heterozygotes compared to the wild-type mice. However, recovery and return of the percentage of kidney cells in S-phase to control levels was seen at 3 weeks. The estimated maximum tolerated dose for longer-term exposures was 15 ppm, based on mortality, induced kidney pathology, and regenerative cell proliferation. A one-year cancer bioassay was initiated with doses of 0, 0.5, 3, 10, and 15 ppm, based on this information. No pathological changes in the livers were found at the 13-week time point of that study. At 13 weeks, the kidney lesions and regenerative cell proliferation seen at the 1-week time point at doses of 10 ppm and above had resolved, and the cell proliferation rates had returned to baseline. Differences in toxicity indicate that caution be used in substituting wild-type mice for transgenic mice for range-finding studies to select doses for p53(+/-) cancer studies. Resolution of the kidney lesions indicates that periods of very high regenerative cell proliferation, potentially important in the carcinogenic process, may not be observed if measurements are taken only at 3 weeks of exposure or later.