Prevalence of medical students' burnout and its associated demographics and lifestyle factors in Hong Kong.

BACKGROUND: Burnout causes personal suffering and adverse professional consequences. It is prevalent among medical students, although the relationship between burnout and lifestyle factors are understudied in Chinese medical students. Thus, this study aims to (i) estimate the prevalence of burnout among medical students in Hong Kong (HK) and (ii) delineate the relationship between burnout and various lifestyle factors. METHOD: 1,341 students were invited to complete a questionnaire from September to December 2017. Burnout was measured by the Maslach Burnout Inventory. Lifestyle factors including drinking habit, sleep habit and quality, and exercise level were assessed by validated instruments, including Alcohol Use Disorder Identification Test (AUDIT-C), Pittsburgh Sleep Quality Index (PSQI), and Godin-Shephard Leisure-Time Physical Activity (GSLTPA), respectively. Smoking status and use of self-medications were also inquired into, while demographic data was self-reported. Prevalence of burnout with confidence intervals was calculated. Difference in lifestyle and demographic data in students with or without burnout, were compared by t-test and Chi-square/Fisher's exact test. From this, all associations with significant p-value at p<0.1 were entered into the multiple logistic regression model. RESULTS: 731 students (55.6%) responded to the questionnaire. Prevalence of burnout was 27.9% (95%CI: 24.6%-31.5%). Only 3 students in the whole sample smoked; and 6.6% of students drank weekly but rarely drank more than 2 drinks per week. 6.3% and 2.3% self-medicated themselves with medications to improve their sleep and concentration, respectively. Using a multiple logistic regression model, only sleep quality and exercise level were significantly associated with the presence of burnout. CONCLUSION: Around a quarter of medical students in HK suffered from burnout. Burnout was found to be significantly associated with sleep quality and physical exercise. The study also highlighted that HK medical students lived very different lifestyles from those from other countries. More research is needed to design and establish the effectiveness of lifestyle interventional programs that enhance exercise level and sleep quality.

Biological disease-modifying antirheumatic drugs in juvenile idiopathic arthritis of polyarticular course, enthesitis-related arthritis, and psoriatic arthritis: a consensus statement.

OBJECTIVES: Juvenile idiopathic arthritis (JIA) is the most common type of inflammatory arthritis in children. Treatment options have been expanded since the introduction of biologics, which are highly effective. The existing local JIA treatment guideline was published more than a decade ago, when use of biologics was not as common. In this article, we review the latest evidence on using biologics in three JIA subtypes: JIA of polyarticular course (pcJIA), enthesitis-related arthritis (ERA), and psoriatic arthritis (PsA). Based on the latest information, an update on eligibility, response assessment, termination, and safety information for using biologics in these patients was performed. CONSENSUS PROCESS: The JIA Work Group, which consisted of nine paediatricians experienced in managing JIA, was convened in 2016. Publications before July 2017 were screened. Eligible articles were clinical trials, extension studies, systemic reviews, and recommendations from international societies and regulatory agencies about the use of biologics in pcJIA, ERA, and PsA. Evidence extraction, appraisal, and drafting of propositions were performed by two reviewers. Extracted evidence and drafted propositions were presented and discussed at the first two meetings. Overwhelming consensus was obtained at the final meeting in May 2018. Seven practice consensus statements were formulated. Regular review should be performed to keep the practice evidence-based and up-to-date.

Novel inhibition of PIM2 kinase has significant anti-tumor efficacy in multiple myeloma.

The PIM kinase family (PIM1, 2 and 3) have a central role in integrating growth and survival signals, and are expressed in a wide range of solid and hematological malignancies. We now confirm that PIM2 is overexpressed in multiple myeloma (MM) patients, and within MM group it is overexpressed in the high-risk MF subset (activation of proto-oncogenes MAF/MAFB). This is consistent with our finding of PIM2's role in key signaling pathways (IL-6, CD28 activation) that confer chemotherapy resistance in MM cells. These studies have identified a novel PIM2-selective non-ATP competitive inhibitor (JP11646) that has a 4 to 760-fold greater suppression of MM proliferation and viability than ATP-competitive PIM inhibitors. This increased efficacy is due not only to the inhibition of PIM2 kinase activity, but also to a novel mechanism involving specific downregulation of PIM2 mRNA and protein expression not seen with the ATP competitive inhibitors. Treatment with JP11646 in xenogeneic myeloma murine models demonstrated significant reduction in tumor burden and increased median survival. Altogether our findings suggest the existence of previously unrecognized feedback loop(s) where PIM2 kinase activity regulates PIM2 gene expression in malignant cells, and that JP11646 represents a novel class of PIM2 inhibitors that interdicts this feedback.

Mitochondrial thioredoxin reductase regulates major cytotoxicity pathways of proteasome inhibitors in multiple myeloma cells.

It is generally accepted that intracellular oxidative stress induced by proteasome inhibitors is a byproduct of endoplasmic reticulum (ER) stress. Here we report a mechanism underlying the ability of proteasome inhibitors bortezomib (BTZ) and carfilzomib (CFZ) to directly induce oxidative and ER stresses in multiple myeloma (MM) cells via transcriptional repression of a gene encoding mitochondrial thioredoxin reductase (TXNRD2). TXNRD2 is critical for maintenance of intracellular red-ox status and detoxification of reactive oxygen species. Depletion of TXNRD2 to the levels detected in BTZ- or CFZ-treated cells causes oxidative stress, ER stress and death similar to those induced by proteasome inhibitors. Reciprocally, restoration of near-wildtype TXNRD2 amounts in MM cells treated with proteasome inhibitors reduces oxidative stress, ER stress and cell death by ~46%, ~35% and ~50%, respectively, compared with cells with unrestored TXNRD2 levels. Moreover, cells from three MM cell lines selected for resistance to BTZ demonstrate elevated levels of TXNRD2, indirectly confirming its functional role in BTZ resistance. Accordingly, ectopic expression of TXNRD2 in MM cell xenografts in immunocompromised mice blunts therapeutic effects of BTZ. Our data identify TXNRD2 as a potentially clinically relevant target, inhibition of which is critical for proteasome inhibitor-dependent cytotoxicity, oxidative stress and ER stress.

Inhalation toxicity study of disk-shaped potassium octatitanate particles (terracess TF) in rats following 90 days of aerosol exposure.

Since fibrous particles such as asbestos and some man-made fibers (MMF) have been known to produce carcinogenic or fibrogenic effects, disk-shaped potassium octatitanate (POT) particles (trade name: Terracess TF) were manufactured as nonfibrous particles. A 90-day inhalation toxicity study of Terracess TF was performed to evaluate comparative inhalation toxicity of the disk shape with a fibrous shape that was previously evaluated. Four groups of 20 male and 15 female rats each were exposed to Terracess TF aerosols at concentrations of 0, 2, 10, or 50 mg/m(3) for 90 days. Ten male and 10 female rats per group were sacrificed at 90 days of exposure. After 90 days of exposure, 5 male rats per group were sacrificed at 3 wk of recovery period and 4-5 male rats per group or 5 female rats per group were sacrificed at 15 wk of recovery for lung clearance and histopathology. The mass median aerodynamic equivalent diameter (MMAED) of the aerosols of test materials ranged from 2.5 to 2.9 microm. There were no test-substance-related adverse effects on clinical observations. At the end of the 90-day exposure, a slight increase in lung-to-body weight ratios was observed at 50 mg/m(3) in male but not in female rats. However, lung weights were within normal limits after 3- or 15-wk recovery periods. Microscopically, inhaled Terracess TF particles were mostly phagocytized by free alveolar macrophages (AMs) in the alveolar airspaces and alveolar walls maintained normal structure at 2 and 10 mg/m(3). At 50 mg/m(3), some alveoli were distended and filled with aggregates of particle-laden AMs. The alveolar walls showed slight type II pneumocyte hyperplasia, but neither proliferative inflammation nor alveolar fibrosis was present at 50 mg/m(3). The clearance half-times for Terracess TF were estimated to be in the order of 6 to 9 mo for the 50-mg/m(3) group and 2 to 3 mo for the 10- and 2-mg/m(3) groups. The lung responses and lung clearance rate were comparable to those of "nuisance" type dusts at these concentrations. Based on interpretation that aggregated particle-laden AMs in alveoli was considered to be an early histopathological sign of lung overloading, an effect level was considered to be 50 mg/m(3) and no-observedadverse- effect level (NOAEL) was 10 mg/m(3). This experiment clearly demonstrated that particle morphology was considered to be an important factor to determine inhaled particle toxicity.

TMPRSS4 promotes invasion, migration and metastasis of human tumor cells by facilitating an epithelial-mesenchymal transition.

TMPRSS4 is a novel type II transmembrane serine protease found at the cell surface that is highly expressed in pancreatic, colon and gastric cancer tissues. However, the biological functions of TMPRSS4 in cancer are unknown. Here we show, using reverse transcription-PCR, that TMPRSS4 is highly elevated in lung cancer tissues compared with normal tissues and is also broadly expressed in a variety of human cancer cell lines. Knockdown of TMPRSS4 by small interfering RNA treatment in lung and colon cancer cell lines was associated with reduction of cell invasion and cell-matrix adhesion as well as modulation of cell proliferation. Conversely, the invasiveness, motility and adhesiveness of SW480 colon carcinoma cells were significantly enhanced by TMPRSS4 overexpression. Furthermore, overexpression of TMPRSS4 induced loss of E-cadherin-mediated cell-cell adhesion, concomitant with the induction of SIP1/ZEB2, an E-cadherin transcriptional repressor, and led to epithelial-mesenchymal transition events, including morphological changes, actin reorganization and upregulation of mesenchymal markers. TMPRSS4-overexpressing cells also displayed markedly increased metastasis to the liver in nude mice upon intrasplenic injection. Taken together, these studies suggest that TMPRSS4 controls the invasive and metastatic potential of human cancer cells by facilitating an epithelial-mesenchymal transition; TMPRSS4 may be a potential therapeutic target for cancer treatment.

Feature subset selection for improving the performance of false positive reduction in lung nodule CAD.

We propose a feature subset selection method based on genetic algorithms to improve the performance of false positive reduction in lung nodule computer-aided detection (CAD). It is coupled with a classifier based on support vector machines. The proposed approach determines automatically the optimal size of the feature set, and chooses the most relevant features from a feature pool. Its performance was tested using a lung nodule database (52 true nodules and 443 false ones) acquired by multislice CT scans. From 23 features calculated for each detected structure, the suggested method determined ten to be the optimal feature subset size, and selected the most relevant ten features. A support vector machine classifier trained with the optimal feature subset resulted in 100% sensitivity and 56.4% specificity using an independent validation set. Experiments show significant improvement achieved by a system incorporating the proposed method over a system without it. This approach can be also applied to other machine learning problems; e.g. computer-aided diagnosis of lung nodules.

Porcine CD80: cloning, characterization, and evidence for its role in direct human T-cell activation.

Previous studies has shown that human anti-pig reactivity in mixed lymphocyte cultures require the indirect presentation of antigens by human antigen presenting cells (APC). Xenoreactivity was inhibited by blockade of human costimulatory molecules. We investigated the role of porcine costimulatory molecules in their ability to activate human T cells directly. Porcine CD80 was cloned from lipopolysaccharide (LPS)-activated porcine lymphocytes. Sequence analysis showed a high degree of conservation in residues involved in CD28/CTLA4. COS cells transfected with porcine CD80 was able to activate human T cells in a cyclosporine independent manner, demonstrating that porcine CD80 can costimulate human T cells. Tumor necrosis factor-alpha (TNF-alpha) activated porcine splenocytes have been shown to up-regulate B7s. In order to test the effect of costimulation blockade in a xeno system, activated splenocytes were cultured with purified CD4+ T cells. The results demonstrated that these cells were capable of activating human T cells and this activation can be blocked by using an antihuman CD80 antibody that demonstrated cross-reactivity to porcine CD80. Non-cross reactive antibodies had no effect, again suggesting direct activation of the human T cells. These data suggest that a reagent that can block both the direct and indirect activation is necessary for a discordant xenotransplant.

Efficient priming of protein antigen-specific human CD4(+) T cells by monocyte-derived dendritic cells.

Dendritic cells (DCs) have the unique ability to initiate an immune response in vivo by capturing antigens (Ags) in peripheral tissues and migrating to secondary lymphoid organs, where they sensitize naive CD4(+) T cells. To mimic this process in vitro, previous studies have shown that DCs directly isolated from peripheral blood can be used to elicit primary responses to neoantigens (neoAgs). In other studies, when monocyte-derived DCs have been utilized to sensitize total CD4(+) T cells in vitro, only secondary proliferation to neoAgs could be elicited. In the present study, the relative abilities of CD40 ligation, protein kinase C activation, and culture in tumor necrosis factor alpha (TNF-alpha) to induce functional and phenotypic maturation of human DCs from monocyte precursors were compared. Optimal TNF-alpha-induced maturation of DCs required a prolonged 4-day culture. It was then found that loading immature DCs with the neoAgs keyhole limpet hemocyanin or human immunodeficiency virus-1 p24 gag prior to TNF-alpha-induced maturation, rather than after maturation, was crucial to sensitize CD4(+) T cells to new Ags. This primary proliferation to neoAgs was initiated from the CD4(+) CD45RA(+) naive T-cell population. Finally, it was found that monocyte-derived DCs acquired the ability to secrete interleukin-12 p70, after contact with Ag-specific T cells. The ability to prime and expand Ag-specific CD4(+) T cells ex vivo to neoAgs in serum-free conditions has potential application for cellular vaccination and adoptive immunotherapy.

Costimulatory molecules are active in the human xenoreactive T-cell response but not in natural killer-mediated cytotoxicity.

BACKGROUND: T-cell costimulatory blocking agents inhibit allospecific T-cell responses in vitro and prevent allograft rejection in vivo. Costimulatory requirements for discordant xenospecific cellular responses remain undefined. We have evaluated costimulatory molecule expression by porcine endothelial cells (PEC) after interaction with human cells and tested agents known to inhibit allospecific responses for their ability to inhibit xenospecific responses in vitro. METHODS: Human-specific agents were screened for their ability to bind porcine costimulatory molecules by FACS. Up-regulation of B7 molecules on PEC was evaluated by FACS after exposure to human cells or supernatants. The effect of human and/or porcine costimulatory blockade was tested in xeno-mixed lymphocyte reactions (XMLRs) and in natural killer (NK) cell cytotoxicity assays. RESULTS: B7 expression was induced on PEC after exposure to human T and NK cells or T cell-conditioned medium. The human XMLR was attenuated by human CTLA4-Ig and anti-human CD154 (hu5C8), and the combination was synergistic. Anti-human CD80 and CD86 antibodies alone had minor effects in the XMLR, but in combination with hu5C8 were as effective as human CTLA4-Ig plus hu5C8. Anti-hCD80 and hCD86 antibodies that did not cross-react with porcine CD80 or CD86 were as effective in blocking the MLR as those that did cross-react, indicating that the predominant costimulation in vitro was derived from the responding cells. None of the agents affected the xeno-NK response. CONCLUSIONS: We conclude that the costimulation-modulating agents block human anti-porcine T-cell responses in vitro predominantly through interruption of costimulation derived from responding cells. They have no effect on NK cell-mediated cytotoxicity.

Immunotoxicity of ethyl carbamate in female BALB/c mice: role of esterase and cytochrome P450.

Ethyl carbamate, a potent carcinogen, has been characterized to be metabolized by cytochrome P450 (P450) and esterase. It has recently been demonstrated that P450 may activate ethyl carbamate to immunotoxic metabolites. To investigate the role of esterase in ethyl carbamate-induced immunosuppression, mice were pretreated intraperitoneally with an esterase inhibitor, diazinon, at 20 mg/kg 30 min prior to the administration of ethyl carbamate intraperitoneally at 100 and 400 mg/kg for 7 consecutive days. Pretreatment with diazinon completely blocked the serum esterase activity. Histopathologically splenic and thymic atrophy was observed when mice were treated with ethyl carbamate, which was potentiated by the pretreatment with diazinon. In spleen, lymphocytes in the periarteriolar lymphoid sheath and the marginal zone appeared to be depleted in the white pulps. In thymus, ethyl carbamate caused a marked depletion of cells in cortex. The antibody response to sheep red blood cells (SRBCs) was more suppressed by ethyl carbamate in diazinon-pretreated groups than in corn oil-pretreated groups. These results suggest that the metabolism of ethyl carbamate by esterase may be an inactivation pathway in ethyl carbamate-induced immunosuppression. In addition, ethyl N-hydroxycarbamate, a P450 metabolite, suppressed the lymphoproliferative response induced by lipopolysaccharide and concanavalin A in splenocyte cultures. These results indicate that the metabolism of ethyl carbamate by P450 may be an activation pathway in immunosuppression by ethyl carbamate.

Evidence for distinct intracellular signaling pathways in CD34+ progenitor to dendritic cell differentiation from a human cell line model.

Intracellular signals that mediate differentiation of pluripotent hemopoietic progenitors to dendritic cells (DC) are largely undefined. We have previously shown that protein kinase C (PKC) activation (with phorbol ester (PMA) alone) specifically induces differentiation of primary human CD34+ hemopoietic progenitor cells (HPC) to mature DC. We now find that cytokine-driven (granulocyte-macrophage CSF and TNF-alpha) CD34+ HPC-->DC differentiation is preferentially blocked by inhibitors of PKC activation. To further identify intracellular signals and downstream events important in CD34+ HPC-->DC differentiation we have characterized a human leukemic cell line model of this process. The CD34+ myelomonocytic cell line KG1 differentiates into dendritic-like cells in response to granulocyte-macrophage CSF plus TNF-alpha, or PMA (with or without the calcium ionophore ionomycin, or TNF-alpha), with different stimuli mediating different aspects of the process. Phenotypic DC characteristics of KG1 dendritic-like cells include morphology (loosely adherent cells with long neurite processes), MHC I+/MHC IIbright/CD83+/CD86+/CD14- surface Ag expression, and RelB and DC-CK1 gene expression. Functional DC characteristics include fluid phase macromolecule uptake (FITC-dextran) and activation of resting T cells. Comparison of KG1 to the PMA-unresponsive subline KG1a reveals differences in expression of TNF receptors 1 and 2; PKC isoforms alpha, beta I, beta II, and mu; and RelB, suggesting that these components/pathways are important for DC differentiation. Together, these findings demonstrate that cytokine or phorbol ester stimulation of KG1 is a model of human CD34+ HPC to DC differentiation and suggest that specific intracellular signaling pathways mediate specific events in DC lineage commitment.

Costimulatory approaches to adoptive immunotherapy.

Costimulation is critical for induction of full T-cell effector function, and thus represents an attractive immunotherapeutic approach for the treatment of cancer. This review examines these approaches, including ex vivo T-cell expansion, systemic "delivery" of constimulation, tumors transduced or transfected with costimulatory ligands, and vaccine strategies using coimmunization with the genes for costimulatory ligands. Impressive results in animal models have been demonstrated and a wide range of human clinical trials are underway.

Bone marrow repopulation by human marrow stem cells after long-term expansion culture on a porcine endothelial cell line.

In vitro exposure of murine hematopoietic stem cells (HSCs) to cell cycle-inducing cytokines has been shown to result in a defect in the ability of these cells to engraft. We used a porcine microvascular endothelial cell (PMVEC) line in conjunction with exogenous interleukin (IL)-3, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF) to expand human HSCs that express the CD34 and Thy-1 antigens but lack lineage-associated markers (CD34+Thy-1+Lin- cells). Ex vivo expansion of hematopoietic cells was evaluated in comparison to stromal cell-free, cytokine-supplemented cultures. Cells expressing the CD34+Thy-1+Lin- phenotype were detectable in both culture systems for up to 3 weeks. These cells were reisolated from the cultures and their ability to engraft human fetal bones implanted into SCID mice (SCID-hu bone) was tested. HSCs expanded in PMVEC coculture were consistently capable of competitive marrow repopulation with multilineage (CD19+ B lymphoid, CD33+ myeloid, and CD34+ cells) progeny present 8 weeks postengraftment. In contrast, grafts composed of cells expanded in stroma-free cultures did not lead to multilineage SCID-hu bone repopulation. Proliferation analysis revealed that by 1 week of culture more than 80% of the cells in the PMVEC cocultures expressing the primitive CD34+CD38- phenotype had undergone cell division. Fewer than 1% of the cells that proliferated in the absence of stromal cells remained CD34+CD38-. These data suggest that the proliferation of HSCs in the presence of IL-3, IL-6, GM-CSF, and SCF without stromal cell support may result in impairment of engraftment capacity, which may be overcome by coculture with PMVECs.

CTLA-4 ligation delivers a unique signal to resting human CD4 T cells that inhibits interleukin-2 secretion but allows Bcl-X(L) induction.

We have assessed the functional effects of a panel of CTLA-4 mAbs on resting human CD4+ T cells. Our results demonstrate that some CTLA-4 mAbs can inhibit proliferative responses of resting CD4+ cells and cell cycle transition from G0 to G1. The inhibitory effects of CTLA-4 were evident within 4 h, at a time when cell surface CTLA-4 expression remained undetectable. Other CTLA-4 mAbs had no detectable inhibitory effects, indicating that binding of Ab to CTLA-4 alone is not sufficient to mediate down-regulation of T cell responses. Interestingly, while IL-2 production was shut off, inhibitory anti-CTLA-4 mAbs permitted induction and expression of the cell survival gene bcl-X(L). Consistent with this observation, cells remained viable and apoptosis was not detected after CTLA-4 ligation.

Phorbol esters induce differentiation of human CD34+ hemopoietic progenitors to dendritic cells: evidence for protein kinase C-mediated signaling.

The intracellular signals that mediate the differentiation of pluripotent hemopoietic progenitors to dendritic cells (DC) are largely undefined. We have found that the phorbol ester PMA by itself induced 47% +/- 8.7% of input human CD34+ hemopoietic progenitors to differentiate into cells with morphology and surface Ag phenotype characteristic of DC by day 7 of culture. Functionally, PMA-generated DC processed and presented whole soluble Ag and also induced resting T cell proliferation and Ag-specific CTL effector function. Unlike cytokine-driven DC differentiation, PMA suppressed proliferation and induced cell death (in part via apoptosis) in cells that did not differentiate to DC. The effects of PMA were blocked by inhibitors of protein kinase C activation, suggesting a central role for this signaling molecule. PMA-mediated signaling also induced expression of the RelB transcription factor, an NF-kappaB family member implicated in DC differentiation. These findings suggest that phorbol esters activate protein kinase C, which then initiates the terminal component of an intracellular signaling pathway(s) involved in the DC differentiation of CD34+ hemopoietic progenitors.

Nucleic acid vaccine-induced immune responses require CD28 costimulation and are regulated by CTLA4.

Immunization with plasmids expressing specific genes (DNA or nucleic acid vaccination (NAV)) elicits robust humoral and cell-mediated immune responses. The mechanisms involved in T cell activation by NAV are incompletely characterized. We have examined the costimulatory requirements of NAV. CD28-deficient mice did not mount Ab or CTL responses following i.m. immunization with eukaryotic expression plasmids encoding the bacterial gene beta-galactosidase (beta gal). Because these mice retained their ability to up-regulate the CTLA4 receptor (a negative regulator of T cell activation), we examined CTLA4's role in the response of wild-type BALB/c mice to NAV. Intact anti-CTLA4 mAb but not Fab fragments suppressed the primary humoral response to pCIA/beta gal without affecting recall responses, indicating CTLA4 activation inhibited Ab production but not T cell priming. Blockade of the ligands for CD28 and CTLA4, CD80 (B7-1) and CD86 (B7-2), revealed distinct and nonoverlapping function. Blockade of CD80 at initial immunization completely abrogated primary and secondary Ab responses, whereas blockade of CD86 suppressed primary but not secondary responses. Simultaneous blockade of CD80 + CD86 was less effective at suppressing Ab responses than either alone. Enhancement of costimulation via coinjection of B7-expressing plasmids augmented CTL responses but not Ab responses, and without evidence of Th1 to Th2 skewing. These findings suggest complex and distinct roles for CD28, CTLA4, CD80, and CD86 in T cell costimulation following nucleic acid vaccination.

Subchronic nasal toxicity of hexamethylphosphoramide administered to rats orally for 90 days.

Rats were administered hexamethylphosphoramide (HMPA) at dosages of 10, 100, 300, and 1000 ppm in drinking water or at 15, 40, or 120 mg/kg/day by gavage for approximately 90 days. Another group of rats was implanted subcutaneously with HMPA-filled osmotic minipumps, designed to deliver a dosage of 40 mg/kg/day to prevent the possibility of direct contact of HMPA with the nasal epithelium. After 90 days at 10 ppm in the drinking water, some rats had tracheas lined with regenerated epithelium, but no HMPA-related lesions were present in any other organs and tissues. At 100 ppm, nasal lesions (epithelial denudation, regeneration, and squamous metaplasia) were mostly in the maxilloturbinates, tips of nasoturbinates, and the adjacent septum in the anterior nasal cavity (level I), but the lesions were confined to the ventral region of the mid-anterior nasal cavity (level II) and to recesses of the posterior nasal cavity (levels III and IV). At 300 ppm, nasal turbinates in level I were partially adhered to the nasal septum by fibrous tissue. In level II the lesions were mainly confined to the ventral medial meatus, but were scattered diffusely in levels III and IV. Denuded turbinates showed minimal bone proliferation. At 1000 ppm, the anterior nasal cavity was partially occluded by extensive adhesion of the turbinates to the nasal septum by granulation tissue and proliferating turbinate bone. The general architecture of the posterior nasal cavity was obliterated by the marked proliferation of turbinate bone and fibrous tissue in the interturbinate spaces. Tracheas showed regenerated epithelium and bronchi had focal epithelial denudation at 100, 300, and 1000 ppm. Foamy alveolar macrophages (histiocytosis) were increased in the lungs at 300 and 1000 ppm. Testicular atrophy occurred at 1000 ppm. No other tissues were affected by HMPA treatment. Nasal lesions in rats given HMPA by gavage were identical in nature to, but sometimes slightly more severe than, the lesions in rats given HMPA in the drinking water. Rats given 40 mg/kg/day HMPA via an osmotic minipump had slightly less severe nasal lesions than did the rats given the same dosage of HMPA by gavage. Testicular atrophy was present in the rats given 120 mg/kg/day by gavage. The results of this study show that, with the exception of bone proliferation, systemic delivery of HMPA or its metabolites to the nasal tissue following oral administration causes tissue damage similar to that caused by direct exposure of the nasal tissue via inhalation. Oral administration of HMPA is a less potent route for producing nasal lesions than is inhalation.