Ion uptake in naturally acidic water

The first studies on ion regulation in fish exposed to low pH, which were inspired by the Acid Rain environmental crisis, seemed to indicate that ion transport at the gills was completely and irreversibly inhibited at pH 4.0-4.5 and below. However, work on characid fish native to the Rio Negro, a naturally acidic, blackwater tributary of the Amazon River, found that they possess ion transport mechanisms that are completely insensitive to pHs as low as 3.25. As more species were examined it appeared that pH-insensitive transport was a trait shared by many, if not most, species in the Order Characiformes. Subsequently, a few other species of fish have been shown to be able to transport ions at low pH, in particular zebrafish (Danio rerio), which show rapid recovery of Na+ uptake at pH 4.0 after initial inhibition. Measurements of rates of Na+ transport during exposure to pharmacological agents that inhibit various transport proteins suggested that characiform fish do not utilize the generally accepted mechanisms for Na+ transport that rely on some form of H+ extrusion. Examination of zebrafish transport at low pH suggest the rapid recovery may be due to a novel Na+/K+ exchanger, but after longer term exposure they may rely on a coupling of Na+/H+ exchangers and NH3 excretion. Further work is needed to clarify these mechanisms of transport and to find other acid-tolerant species to fully gain an appreciation of the diversity of physiological mechansisms involved.

Effect of water calcium, copper, and silver on branchial Na+ permeability in a characid and cichlid fish

We tested the hypothesis that water Ca2+ is involved in control of branchial Na+ permeability in low pH tolerant convict cichlids and black neon tetras. We measured Na+ efflux in water with different Ca2+ concentrations during exposure to low pH, silver, and copper, at levels which are known to stimulate Na+ efflux. For convict cichlids at pH 7.5 exposure to 0 μmol L-1 Ca2+caused Na+ efflux to rise 2.5 times above controls at 100 μmol L-1 Ca2+. However, raising [Ca2+] to 500 μmol L-1 had no effect. Upon exposure to pH 3.5 (control [Ca2+]) Na+ efflux rose almost 5× and increasing the [Ca2+] 5-fold did not reduce the magnitude of stimulation. Exposure to 1 μmol L-1 silver and 25 μmol L-1 copper stimulated Na+ efflux 7×, and 2×, respectively. Raising [Ca2+] concentration during metal exposure halved the stimulation of Na+ efflux caused by silver, and eliminated the stimulation elicited by copper. For black neon tetras raising or lowering water [Ca2+] had no effect on Na+ efflux at pH 7.5. Exposure to pH 3.5 caused Na+ efflux to rise 2.5× but changing [Ca2+] had no effect. Exposure to 1 μmol L-1 silver, or 25 μmol L-1 copper caused Na+ efflux of tetras to rise 4-fold and 3-fold, respectively. Raising [Ca2+] during silver exposure reduced the stimulation of Na+ efflux by about 50%, but during copper exposure increased [Ca2+] had no effect on stimulation of Na+ efflux. These results suggest water Ca2+ plays a role in control of branchial Na+ permeability in cichlids, but perhaps not tetras. In addition, the silver and copper concentrations required to inhibit Na+ uptake and stimulate Na+ efflux were higher than the concentrations used on non-characids and non-cichlids, which indicates that our fish are much more tolerant of these metals.

Microneedle array delivery of Yersinia pestis recapitulates bubonic plague

Fleas transmit Yersinia pestis directly within the dermis of mammals to cause bubonic plague. Syringe-mediated inoculation is widely used to recapitulate bubonic plague and study Y. pestis pathogenesis. However, intradermal needle inoculation is tedious, error prone, and poses a significant safety risk for laboratorians. Microneedle arrays (MNAs) are micron-scale polymeric structures that deliver materials to the dermis, while minimizing the risk of needle sticks. We demonstrated that MNA inoculation is a viable strategy to recapitulate bubonic plague and study bacterial virulence by defining the parameters needed to establish a lethal infection in the mouse model and characterizing the course of infection using live-animal optical imaging. Using MNAs, we also demonstrated that Y. pestis must overcome calprotectin-mediated zinc restriction within the dermis and dermal delivery of an attenuated mutant has vaccine potential. Together, these data demonstrate that MNAs are a safe alternative to study Y. pestis pathogenesis in the laboratory.

Association between bisphosphonate use and COVID-19 related outcomes

Background

Although there are several efficacious vaccines against COVID-19, vaccination rates in many regions around the world remain insufficient to prevent continued high disease burden and emergence of viral variants. Repurposing of existing therapeutics that prevent or mitigate severe COVID-19 could help to address these challenges. The objective of this study was to determine whether prior use of bisphosphonates is associated with reduced incidence and/or severity of COVID-19.

Methods

A retrospective cohort study utilizing payer-complete health insurance claims data from 8,239,790 patients with continuous medical and prescription insurance January 1, 2019 to June 30, 2020 was performed. The primary exposure of interest was use of any bisphosphonate from January 1, 2019 to February 29, 2020. Bisphosphonate users were identified as patients having at least one bisphosphonate claim during this period, who were then 1:1 propensity score-matched to bisphosphonate non-users by age, gender, insurance type, primary-care-provider visit in 2019, and comorbidity burden. Main outcomes of interest included: (a) any testing for SARS-CoV-2 infection; (b) COVID-19 diagnosis; and (c) hospitalization with a COVID-19 diagnosis between March 1, 2020 and June 30, 2020. Multiple sensitivity analyses were also performed to assess core study outcomes amongst more restrictive matches between BP users/non-users, as well as assessing the relationship between BP-use and other respiratory infections (pneumonia, acute bronchitis) both during the same study period as well as before the COVID outbreak.

Results

A total of 7,906,603 patients for whom continuous medical and prescription insurance information was available were selected. A total of 450,366 bisphosphonate users were identified and 1:1 propensity score-matched to bisphosphonate non-users. Bisphosphonate users had lower odds ratios (OR) of testing for SARS-CoV-2 infection (OR = 0.22; 95%CI:0.21-0.23; p<0.001), COVID-19 diagnosis (OR = 0.23; 95%CI:0.22-0.24; p<0.001), and COVID-19-related hospitalization (OR = 0.26; 95%CI:0.24-0.29; p<0.001). Sensitivity analyses yielded results consistent with the primary analysis. Bisphosphonate-use was also associated with decreased odds of acute bronchitis (OR = 0.23; 95%CI:0.22-0.23; p<0.001) or pneumonia (OR = 0.32; 95%CI:0.31-0.34; p<0.001) in 2019, suggesting that bisphosphonates may protect against respiratory infections by a variety of pathogens, including but not limited to SARS-CoV-2.

Conclusions

Prior bisphosphonate-use was associated with dramatically reduced odds of SARS-CoV-2 testing, COVID-19 diagnosis, and COVID-19-related hospitalizations. Prospective clinical trials will be required to establish a causal role for bisphosphonate-use in COVID-19-related outcomes.

Funding

This study was supported by NIH grants, AR068383 and AI155865, a grant from MassCPR (to UHvA) and a CRI Irvington postdoctoral fellowship, CRI2453 (to PH).

Multimodal control of dendritic cell functions by nociceptors

It is known that interactions between nociceptors and dendritic cells (DCs) can modulate immune responses in barrier tissues. However, our understanding of the underlying communication frameworks remains rudimentary. Here, we show that nociceptors control DCs in three molecularly distinct ways. First, nociceptors release the calcitonin gene-related peptide that imparts a distinct transcriptional profile on steady-state DCs characterized by expression of pro-interleukin-1β and other genes implicated in DC sentinel functions. Second, nociceptor activation induces contact-dependent calcium fluxes and membrane depolarization in DCs and enhances their production of proinflammatory cytokines when stimulated. Finally, nociceptor-derived chemokine CCL2 contributes to the orchestration of DC-dependent local inflammation and the induction of adaptive responses against skin-acquired antigens. Thus, the combined actions of nociceptor-derived chemokines, neuropeptides, and electrical activity fine-tune DC responses in barrier tissues.

Quo vadis, neutrophil?

Neutrophil recruitment from blood into tissues is a hallmark of inflammation and anti-microbial host defense. In this issue, De Giovanni et al. describe an unanticipated role for a serotonin metabolite, 5-HIAA, which is produced by activated platelets and mast cells and engages the orphan receptor, GPR35, to recruit neutrophils to inflamed tissues.

Constitutive immune surveillance of the nasal mucosa by neutrophils

The nasal mucosa is a versatile tissue where functions such as olfaction and conditioning of air take place. A particularly relevant and less explored function of this tissue relates to its capacity to respond to insult. Air-borne pathogens can use the nasal mucosa as a portal of entry to further disseminate into deeper tissues and little is known about the immune cell populations these pathogens encounter upon infection. We asked what immune cell populations are present in the murine nasal mucosa and unexpectedly found extravascular neutrophils to be a constitutive and prominent population in the steady state. These neutrophils were found in comparable numbers in conventional vs. germ-free mice and can be divided into three well-defined populations based on the expression of specific cell surface markers and mRNA transcript profiles. One of the populations was traced to nasal mucosa-associated pockets of bone marrow and determined to contribute to the nasal mucosa neutrophil extravascular pool. A second population was found to preferentially phagocytose bacteria during infection. In the absence of infection, this population differentiates into a third population, which interacts with other cells of the nasal mucosa in a manner that resembles trogocytosis. Lastly, we found extravascular granulocyte hematopoietic precursors in the nasal mucosa that likely contribute to the extravascular neutrophil pool. Thus, the nasal mucosa encompasses a constitutive population of extravascular neutrophils that show diverse origins and specialization of function. These findings contribute to our understanding of the composition and development of the microenvironment that air-borne pathogens encounter upon infection in the nasal mucosa.

Examination of ionoregulatory characteristics of South American cichlids

We examined ionoregulatory traits of four cichlid species from South America, oscars (Astronotus ocellatus), Tapajos cichlids (Geophagus sp.), Macmaster's dwarf cichlids (Apistogramma macmasteri), and keyhole cichlids (Cleithracara maronii), all inhabitants of ion-poor waters. K_m values for Na⁺ transport in fish held in 100 μmol L^-1 Na⁺ water ranged from 49 to 143 μmol L^-1, and J_max values spanned 450 to 1205 nmol g^-1 h^-1. After one month in 1000 μmol L^-1 Na⁺ water, kinetic parameters for Na⁺ uptake in three of the four species acclimated, but only oscars displayed the "typical" pattern of higher K_m and lower J_max values. Low pH water inhibited Na⁺ uptake (J_in^Na) in all, and stimulated Na⁺ efflux (J_out^Na) 2.5 to 3.5-fold in three of the four species. Oscars alone had had a measurable J_in^Na at pH 3.5 and no stimulation of J_out^Na. We measured J_in^Na in oscars and keyhole cichlids during exposure to 100 μmol L^-1 Ethoxzolemide (EZ), an inhibitor of carbonic anhydrase, and 1 mmol L^-1 NH₄Cl (HEA). EZ inhibited J_in^Na by about 50% and HEA reduced J_in^Na by 80-90%. These results suggest that Na⁺ uptake involves H⁺ extrusion. Acute exposure to 1 μmol L^-1 CuSO₄ and 60 nmol L^-1 AgNO₃ inhibited J_in^Na in both species by 30-85%. Exposure of oscars to 5-fold higher concentrations of both metals did not further inhibit J_in^Na, but it did stimulate J_out^Na 50-150%. The response to metals of both species are similar to other species that have been examined.

Immunology-Guided Biomaterial Design for Mucosal Cancer Vaccines

Cancer of mucosal tissues is a major cause of worldwide mortality for which only palliative treatments are available for patients with late-stage disease. Engineered cancer vaccines offer a promising approach for inducing antitumor immunity. The route of vaccination plays a major role in dictating the migratory pattern of lymphocytes, and thus vaccine efficacy in mucosal tissues. Parenteral immunization, specifically subcutaneous and intramuscular, is the most common vaccination route. However, this induces marginal mucosal protection in the absence of tissue-specific imprinting signals. To circumvent this, the mucosal route can be utilized, however degradative mucosal barriers must be overcome. Hence, vaccine administration route and selection of materials able to surmount transport barriers are important considerations in mucosal cancer vaccine design. Here, an overview of mucosal immunity in the context of cancer and mucosal cancer clinical trials is provided. Key considerations are described regarding the design of biomaterial-based vaccines that will afford antitumor immune protection at mucosal surfaces, despite limited knowledge surrounding mucosal vaccination, particularly aided by biomaterials and mechanistic immune-material interactions. Finally, an outlook is given of how future biomaterial-based mucosal cancer vaccines will be shaped by new discoveries in mucosal vaccinology, tumor immunology, immuno-therapeutic screens, and material-immune system interplay.

Gamma Interferon Is Required for Chlamydia Clearance but Is Dispensable for T Cell Homing to the Genital Tract

While there is no effective vaccine against Chlamydia trachomatis infection, previous work has demonstrated the importance of C. trachomatis-specific CD4+ T cells (NR1 T cells) in pathogen clearance. Specifically, NR1 T cells have been shown to be protective in mice, and this protection depends on the host's ability to sense the cytokine gamma interferon (IFN-γ). However, it is unclear what role NR1 production or sensing of IFN-γ plays in T cell homing to the genital tract or T cell-mediated protection against C. trachomatis Using two-photon microscopy and flow cytometry, we found that naive wild-type (WT), IFN-γ-/-, and IFN-γR-/- NR1 T cells specifically home to sections in the genital tract that contain C. trachomatis We also determined that protection against infection requires production of IFN-γ from either NR1 T cells or endogenous cells, further highlighting the importance of IFN-γ in clearing C. trachomatis infection.IMPORTANCEChlamydia trachomatis is an important mucosal pathogen that is the leading cause of sexually transmitted bacterial infections in the United States. Despite this, there is no vaccine currently available. In order to develop such a vaccine, it is necessary to understand the components of the immune response that can lead to protection against this pathogen. It is well known that antigen-specific CD4+ T cells are critical for Chlamydia clearance, but the contexts in which they are protective or not protective are unknown. Here, we aimed to characterize the importance of gamma interferon production and sensing by T cells and the effects on the immune response to C. trachomatis Our work here helps to define the contexts in which antigen-specific T cells can be protective, which is critical to our ability to design an effective and protective vaccine against C. trachomatis.

Intercontinental collaborative experience with abdominal, retroperitoneal and pelvic schwannomas

Background

Schwannomas are rare tumours that pose a significant management challenge in the abdomen, retroperitoneum and pelvis. No data are available to inform management strategy.

Methods

A collaborative international cohort study, across specialist sarcoma units, was conducted to include adults presenting between 2000 and 2017 with histopathologically confirmed schwannomas within the abdomen, retroperitoneum or pelvis.

Results

Of 485 patients across 12 centres, 38 (7·8 per cent) were discharged without follow-up, 199 (41·0 per cent) underwent early resection and 248 (51·1 per cent) had radiological monitoring. Of these 248 patients, 96 (38·7 per cent) eventually had surgery, giving an overall resection rate of 60·8 per cent (295 of 485). At baseline, median tumour volume was 90·1 (i.q.r. 26·5–262·0) cm3. The estimated growth rate was 10·5 (95 per cent c.i. 9·4 to 11·6) per cent per year, and was consistent in the short term (within 2 years of diagnosis) and long term (beyond 2 years) (ρ = 0·405, P = 0·021). A decision to operate was more common in symptomatic patients (P &lt; 0·001) and for rapidly growing tumours (growth rate more than 20 per cent per year) (P = 0·025). R0/R1 resection was achieved in 91·6 per cent of patients (263 of 287). Kaplan–Meier long-term recurrence rates after R0/R1 resection were 2·3 and 6·7 per cent at 3 and 5 years respectively.

Conclusion

Specific recommendations include: indications for early surgery, prediction of growth from radiological monitoring, promotion of selective submacroscopic resection and cessation of postoperative imaging surveillance.

Mucosal absorption of therapeutic peptides by harnessing the endogenous sorting of glycosphingolipids

Transport of biologically active molecules across tight epithelial barriers is a major challenge preventing therapeutic peptides from oral drug delivery. Here, we identify a set of synthetic glycosphingolipids that harness the endogenous process of intracellular lipid-sorting to enable mucosal absorption of the incretin hormone GLP-1. Peptide cargoes covalently fused to glycosphingolipids with ceramide domains containing C6:0 or smaller fatty acids were transported with 20-100-fold greater efficiency across epithelial barriers in vitro and in vivo. This was explained by structure-function of the ceramide domain in intracellular sorting and by the affinity of the glycosphingolipid species for insertion into and retention in cell membranes. In mice, GLP-1 fused to short-chain glycosphingolipids was rapidly and systemically absorbed after gastric gavage to affect glucose tolerance with serum bioavailability comparable to intraperitoneal injection of GLP-1 alone. This is unprecedented for mucosal absorption of therapeutic peptides, and defines a technology with many other clinical applications.

Dissemination of a highly virulent pathogen: tracking the early events that define infection

The series of events that occurs immediately after pathogen entrance into the body is largely speculative. Key aspects of these events are pathogen dissemination and pathogen interactions with the immune response as the invader moves into deeper tissues. We sought to define major events that occur early during infection of a highly virulent pathogen. To this end, we tracked early dissemination of Yersinia pestis, a highly pathogenic bacterium that causes bubonic plague in mammals. Specifically, we addressed two fundamental questions: (1) do the bacteria encounter barriers in disseminating to draining lymph nodes (LN), and (2) what mechanism does this nonmotile bacterium use to reach the LN compartment, as the prevailing model predicts trafficking in association with host cells. Infection was followed through microscopy imaging in addition to assessing bacterial population dynamics during dissemination from the skin. We found and characterized an unexpected bottleneck that severely restricts bacterial dissemination to LNs. The bacteria that do not pass through this bottleneck are confined to the skin, where large numbers of neutrophils arrive and efficiently control bacterial proliferation. Notably, bottleneck formation is route dependent, as it is abrogated after subcutaneous inoculation. Using a combination of approaches, including microscopy imaging, we tested the prevailing model of bacterial dissemination from the skin into LNs and found no evidence of involvement of migrating phagocytes in dissemination. Thus, early stages of infection are defined by a bottleneck that restricts bacterial dissemination and by neutrophil-dependent control of bacterial proliferation in the skin. Furthermore, and as opposed to current models, our data indicate an intracellular stage is not required by Y. pestis to disseminate from the skin to draining LNs. Because our findings address events that occur during early encounters of pathogen with the immune response, this work can inform efforts to prevent or control infection.

The earliest stage of any infection takes place when a pathogen enters the body (inoculation) at an initial site of contact. From this point, the pathogen can spread into deeper tissues where the pathogen itself and the immune responses against it cause disease. Very little is known about the events that follow inoculation and how pathogens move from the initial site of contact into deeper tissues. A better understanding of this process can potentially result in strategies to control or prevent disease. We studied the highly infectious bacterium that causes bubonic plague (Yersinia pestis) and how it spreads inside the body, from the skin into lymph nodes. We found that movement from the skin is highly restricted as only a small fraction of the bacteria that are deposited into this tissue are found in lymph nodes. While it is currently thought that Y. pestis spreads from the skin inside trafficking cells of the innate immune response, our work suggests these cells are not required for the bacteria to move into lymph nodes. Our findings can influence vaccine development efforts as these strategies are based on the study of early pathogen interactions with cells of the immune response.

Elimination of Onchocerca volvulus Transmission in the Huehuetenango Focus of Guatemala

In Latin America, onchocerciasis is targeted for elimination by 2012 through twice-yearly mass treatment of the eligible population with ivermectin. In Guatemala, two of the four historical endemic foci have demonstrated elimination of transmission, following World Health Organization guidelines. Using established guidelines ophthalmological, serological, and entomological evaluations were conducted in 2007-8 to determine the transmission status of onchocerciasis in the Huehuetenango focus. The prevalence of Onchocerca volvulus microfilariae in the anterior segment of the eye in 365 residents was 0% (95% confidence interval [CI] 0-0.8%), the prevalence of infection of O. volvulus in Simulium ochraceum among 8252 flies collected between November 2007 and April 2008 was 0% (95% CI 0-0.02%), and the prevalence of antibodies to a recombinant O. volvulus antigen in 3118 school age children was 0% (95% CI 0-0.1%). These results showed transmission interruption; thus, in 2009 mass treatment was halted and posttreatment surveillance began. To verify for potential recrudescence an entomological evaluation (from December 2010 to April 2011) was conducted during the 2nd and 3rd year of posttreatment surveillance. A total of 4587 S. ochraceum were collected, and the prevalence of infection of O. volvulus was 0% (95% CI 0-0.04%). Transmission of onchocerciasis in the Huehuetenango focus has been eliminated.

Bioluminescence imaging to track bacterial dissemination of Yersinia pestis using different routes of infection in mice

BACKGROUND

Plague is caused by Yersinia pestis, a bacterium that disseminates inside of the host at remarkably high rates. Plague bacilli disrupt normal immune responses in the host allowing for systematic spread that is fatal if left untreated. How Y. pestis disseminates from the site of infection to deeper tissues is unknown. Dissemination studies for plague are typically performed in mice by determining the bacterial burden in specific organs at various time points. To follow bacterial dissemination during plague infections in mice we tested the possibility of using bioluminescence imaging (BLI), an alternative non-invasive approach. Fully virulent Y. pestis was transformed with a plasmid containing the luxCDABE genes, making it able to produce light; this lux-expressing strain was used to infect mice by subcutaneous, intradermal or intranasal inoculation.

RESULTS

We successfully obtained images from infected animals and were able to follow bacterial dissemination over time for each of the three different routes of inoculation. We also compared the radiance signal from animals infected with a wild type strain and a Δcaf1ΔpsaA mutant that we previously showed to be attenuated in colonization of the lymph node and systemic dissemination. Radiance signals from mice infected with the wild type strain were larger than values obtained from mice infected with the mutant strain (linear regression of normalized values, P<0.05).

CONCLUSIONS

We demonstrate that BLI is useful for monitoring dissemination from multiple inoculation sites, and for characterization of mutants with defects in colonization or dissemination.

Impact of ontogenetic changes in branchial morphology on gill function in Arapaima gigas

Soon after hatching, the osteoglossid fish Arapaima gigas undergoes a rapid transition from a water breather to an obligate air breather. This is followed by a gradual disappearance of gill lamellae, which leaves smooth filaments with a reduced branchial diffusion capacity due to loss of surface area, and a fourfold increase in diffusion distance. This study evaluated the effects these changes have on gill function by examining two size classes of fish that differ in gill morphology. In comparison to smaller fish (approximately 67.5 g), which still have lamellae, larger fish (approximately 724.2 g) without lamellae took up a slightly greater percentage of O2 across the gills (30.1% vs. 23.9%), which indicates that the morphological changes do not place limitations on O2 uptake in larger fish. Both size groups excreted similar percentages of CO2 across the gills (85%-90%). However, larger fish had higher blood PCO2 (26.51.9 vs. 16.51.5 mmHg) and HCO3(-) (40.2 +/- 2.9 vs. 33.6 +/- 4.5 mmol L(-1)) concentrations and lower blood pH (7.58 +/- 0.01 vs. 7.70 +/- 0.04) than did smaller fish, despite having lower mass-specific metabolisms, suggesting a possible diffusion limitation for CO2 excretion in larger fish. With regard to ion regulation, rates of diffusive Na+ loss were about 3.5 times higher in larger fish than they were in smaller fish, despite the lowered branchial diffusion capacity, and rates of Na+ uptake were higher by about the same amount despite 40% lower activity of branchial Na+/K+-ATPase. Kinetic analysis of Na uptake revealed an extremely low-affinity (K(m) = 587.9 +/- 169.5 micromol L(-1)), low-capacity (J(max) = 265.7 +/- 56.8 nmol g(-1) h(-1)) transport system. These data may reflect a general reduction in the role of the gills in ion balance. Renal Na+/K+-ATPase activity was 5-10 times higher than Na+/K+-ATPase activity in the gills, and urine: plasma ratios for Na+ and Cl(-) were very low (0.001-0.005) relative to that of other fish, which suggested an increased role for dietary salt intake and renal salt retention and which was representative of a more "terrestrial" mode of ion regulation. Such de-emphasis of branchial ion regulation confers greatly reduced sensitivity of diffusive ion loss to low water pH. Ammonia excretion also appeared to be impacted by gill changes. Rates of ammonia excretion in larger fish were one third less than that in smaller fish, despite larger fish having blood ammonia concentrations that were twice as high.

Exposure of seasonal migrant workers to Onchocerca volvulus on coffee plantations in Guatemala

Onchocerciasis (river blindness), which is close to being eliminated from Guatemala through semiannual administration of ivermectin, is still transmitted in one area of the country that coincidentally receives an annual influx of migrant workers to harvest coffee. Migrant workers generally are not included in semiannual ivermectin treatments, but if infected could serve as a reservoir. We report on two studies undertaken to measure the exposure to onchocerciasis (presence of IgG4 antibodies to a recombinant Onchocerca volvulus antigen, OV-16) among migrant workers. During two coffee harvest seasons, 170 migrant workers with a history of working in the disease-endemic area were tested and 1 (0.6%, 95% confidence interval = 0-3.2%) was seropositive. This low rate of exposure in migrant workers indicates that they are unlikely to play a significant role in transmission of onchocerciasis and may indicate that transmission in the last remaining disease-endemic area of Guatemala is decreasing significantly.

Successful interruption of transmission of Onchocerca volvulus in the Escuintla-Guatemala focus, Guatemala

BACKGROUND

Elimination of onchocerciasis (river blindness) through mass administration of ivermectin in the six countries in Latin America where it is endemic is considered feasible due to the relatively small size and geographic isolation of endemic foci. We evaluated whether transmission of onchocerciasis has been interrupted in the endemic focus of Escuintla-Guatemala in Guatemala, based on World Health Organization criteria for the certification of elimination of onchocerciasis.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted evaluations of ocular morbidity and past exposure to Onchocerca volvulus in the human population, while potential vectors (Simulium ochraceum) were captured and tested for O. volvulus DNA; all of the evaluations were carried out in potentially endemic communities (PEC; those with a history of actual or suspected transmission or those currently under semiannual mass treatment with ivermectin) within the focus. The prevalence of microfilariae in the anterior segment of the eye in 329 individuals (> or =7 years old, resident in the PEC for at least 5 years) was 0% (one-sided 95% confidence interval [CI] 0-0.9%). The prevalence of antibodies to a recombinant O. volvulus antigen (Ov-16) in 6,432 school children (aged 6 to 12 years old) was 0% (one-sided 95% IC 0-0.05%). Out of a total of 14,099 S. ochraceum tested for O. volvulus DNA, none was positive (95% CI 0-0.01%). The seasonal transmission potential was, therefore, 0 infective stage larvae per person per season.

CONCLUSIONS/SIGNIFICANCE

Based on these evaluations, transmission of onchocerciasis in the Escuintla-Guatemala focus has been successfully interrupted. Although this is the second onchocerciasis focus in Latin America to have demonstrated interruption of transmission, it is the first focus with a well-documented history of intense transmission to have eliminated O. volvulus.

Metabolic and ionoregulatory responses of the Amazonian cichlid, Astronotus ocellatus, to severe hypoxia

We examined the metabolic and ionoregulatory responses of the Amazonian cichlid, Astronotus ocellatus, to 20 h exposure to severe hypoxia (0.37 +/- 0.19 mg O(2)/l; 4.6% air saturation) or 8 h severe hypoxia followed by 12 h recovery in normoxic water. During 20 h exposure to hypoxia, white muscle [ATP] was maintained at normoxic levels primarily through a 20% decrease in [creatine phosphate] (CrP) and an activation of glycolysis yielding lactate accumulation. Muscle lactate accumulation maintained cytoplasmic redox state ([NAD(+)]/[NADH]) and was associated with an inactivation of the mitochondrial enzyme pyruvate dehydrogenase (PDH). The inactivation of PDH was not associated with significant changes in cytoplasmic allosteric modulators ([ADP(free)], redox state, or [pyruvate]). Hypoxia exposure caused an approximately 65% decrease in gill Na(+)/K(+) ATPase activity, which was not matched by changes in Na(+)/K(+) ATPase alpha-subunit protein abundance indicating post-translational modification of Na(+)/K(+) ATPase was responsible for the decrease in activity. Despite decreases in gill Na(+)/K(+) ATPase activity, plasma [Na(+)] increased, but this increase was possibly due to a significant hemoconcentration and fluid shift out of the extracellular space. Hypoxia caused an increase in Na(+)/K(+) ATPase alpha-subunit mRNA abundance pointing to either reduced mRNA degradation during exposure to hypoxia or enhanced expression of Na(+)/K(+) ATPase alpha-subunit relative to other genes.

Physiological responses to hyper-saline waters in sailfin mollies (Poecilia latipinna)

We examined the ionoregulatory physiology and biochemistry of the teleost sailfin molly (Poecilia latipinna), an inhabitant of salt marshes along the gulf coast, during exposure to hyper-saline waters (salinity range 35-95 ppt). Mollies were able to tightly control plasma Na(+) and Cl(-) concentrations and tissue water levels up to 65 ppt, but at higher salinities plasma ion levels began to rise and muscle water content dropped. Still, even at the highest salinity (90 ppt) plasma Na(+) and Cl(-) levels were only 32% and 39%, respectively, above levels at 35 ppt. Drinking rates at 60 ppt climbed 35%, while gut Na(+)/K(+)-ATPase (NAK) activity rose 70% and branchial NAK activity jumped 200%. The relatively small rise in drinking rate, in the face of a more than doubling of the osmotic gradient, suggests that a reduction in branchial water permeability significantly limited water loss and associated salt load. At 80 ppt, a salinity where plasma ion levels just begin to rise, drinking rate rose more rapidly, but gut and gill NAK activity did not, suggesting that mollies employed other pathways (perhaps renal) of salt excretion. At higher salinities, plasma ion levels continued to rise and muscle water content fell slightly indicating the beginnings of internal osmotic disturbances. To evaluate the energetic costs of hyper-salinity on mollies we measured the rate of O(2) consumption and found it rose with salinity, in sharp contrast to virtually all species previously examined. Interestingly, despite higher metabolism, growth was unaffected by hyper-salinity.

Limited extracellular but complete intracellular acid-base regulation during short-term environmental hypercapnia in the armoured catfish, Liposarcus pardalis

Environmental hypercapnia induces a respiratory acidosis that is usually compensated within 24-96 h in freshwater fish. Water ionic composition has a large influence on both the rate and degree of pH recovery during hypercapnia. Waters of the Amazon are characteristically dilute in ions, which may have consequences for acid-base regulation during environmental hypercapnia in endemic fishes. The armoured catfish Liposarcus pardalis, from the Amazon, was exposed to a water P(CO(2)) of 7, 14 or 42 mmHg in soft water (in micromol l(-1): Na(+), 15, Cl(-), 16, K(+), 9, Ca(2+), 9, Mg(2+), 2). Blood pH fell within 2 h from a normocapnic value of 7.90+/-0.03 to 7.56+/-0.04, 7.34+/-0.05 and 6.99+/-0.02, respectively. Only minor extracellular pH (pH(e)) recovery was observed in the subsequent 24-96 h. Despite the pronounced extracellular acidosis, intracellular pH (pH(i)) of the heart, liver and white muscle was tightly regulated within 6 h (the earliest time at which these parameters were measured) via a rapid accumulation of intracellular HCO(3)(-). While most fish regulate pH(i) during exposure to environmental hypercapnia, the time course for this is usually similar to that for pH(e) regulation. The degree of extracellular acidosis tolerated by L. pardalis, and the ability to regulate pH(i) in the face of an extracellular acidosis, are the greatest reported to date in a teleost fish. The preferential regulation of pH(i) in the face of a largely uncompensated extracellular acidosis in L. pardalis is rare among vertebrates, and it is not known whether this is associated with the ability to air-breathe and tolerate aerial exposure, or living in water dilute in counter ions, or with other environmental or evolutionary selective pressures. The ubiquity of this strategy among Amazonian fishes and the mechanisms employed by L. pardalis are clearly worthy of further study.

Neutrophil apoptosis is delayed by trauma patients' plasma via a mechanism involving proinflammatory phospholipids and protein kinase C

BACKGROUND

Delayed apoptosis of primed neutrophils (PMNs) may facilitate PMN-mediated tissue injury leading to multiple organ failure (MOF). We previously reported delayed apoptosis and priming of PMNs in severely injured patients at risk for MOF. Our in vitro and in vivo data have implicated phospholipids in PMN cytotoxicity following trauma and shock. The phospholipid signaling pathway remains to be elucidated, but may involve protein kinase C (PKC). We hypothesized that circulating platelet-activating factor (PAF) and PAF-like proinflammatory phospholipids mediate delayed postinjury PMN apoptosis and that PKC is integral to the signaling pathway.

METHODS

Blood was drawn from severely injured patients (n = 6; mean injury severity score = 21 and transfusion = 10 units) at 6 h postinjury. The plasma fraction was isolated and incubated (5% CO(2), 37 degrees C, 24 h) with PMNs harvested from healthy volunteers. Some PMNs were preincubated with a PAF receptor antagonist (WEB 2170, 400 microM) or a PKC inhibitor (Bis I, 1 microM). Apoptotic index (% PMNs undergoing apoptosis) was assessed morphologically.

RESULTS

Trauma patients' plasma delayed PMN apoptosis compared with plasma from controls. The PMN apoptotic index was not altered by WEB 2170 or Bis I alone; however, WEB 2170 or Bis I pretreatment abrogated delayed PMN apoptosis in response to trauma patients' plasma.

CONCLUSION

Trauma patients' plasma delays apoptosis of PMNs. Our data implicate PAF-like phospholipids in this effect, and PKC appears to be integral in the signaling process. Further elucidation of specific lipids and signaling pathways may reveal clinically accessible therapeutic targets to prevent PMN-mediated hyperinflammation.

Protection by natural blackwater against disturbances in ion fluxes caused by low pH exposure in freshwater stingrays endemic to the Rio Negro

Stenohaline freshwater stingrays (Potamotrygon spp.) are endemic to the very dilute (Na(+), Cl(-), Ca2(+) <or=30 micromol L(-1)), often acidic blackwaters of the Rio Negro despite gill Na(+) and Cl(-) transport characteristics that appear unfavorable (high K(m), low J(max)). We evaluated the possible protective role of blackwater itself, which is rich in dissolved organic carbon (DOC), as well as the importance of Ca(2+) in allowing this tolerance of dilute, acidic conditions. Responses of stingrays in natural blackwater (DOC=8.4 mg L(-1)) were compared with those in a natural reference water with similar ion levels but low DOC (0.6 mg L(-1)). Comparing these two water types, we found that differences in Na(+) and Cl(-) unidirectional fluxes (JXin, JXout; measured with radiotracers) and net fluxes (JXnet), influx and outflux kinetic relationships, and net ammonia excretion (J(Amm)) were generally small at pH 6.3, though the balance points where Jin=Jout shifted from >300 micromol L(-1) in reference water (low DOC) to about 100 micromol L(-1) in blackwater (high DOC). In reference water, both JNain and JClin were inhibited >90%, both JNaout and JClout more than doubled, and J(Amm) did not change at pH 4.0. In blackwater, the inhibition of influxes was attenuated, the increases in outflux did not occur, and J(Amm) increased by 60% at pH 4.0. Addition of 100 micromol L(-1) Ca(2+) to reference water prevented the increases in JNaout and JClout and allowed J(Amm) to increase at pH 4.0, which demonstrates that the gills are sensitive to Ca(2+). However, addition of Ca(2+) to blackwater had no effect on the responses to pH 4.0. Addition of commercial humic acid to reference water did not duplicate the effects of natural Rio Negro blackwater at the same DOC level; instead, it greatly exacerbated the increases in JNaout and JClout at low pH and prevented any protective influence of added Ca(2+). Thus, blackwater DOC appears to be very different from commercial humic acid. Biogeochemical modeling indicated that blackwater DOC prevents Ca(2+) binding, but not H(+) binding, to the gills and that the protective effects of blackwater cannot be attributed to its higher buffer capacity or its elevated Al or Fe levels. Natural DOC may act directly at the gills at low pH to exert a protective effect and, when doing so, may override any protective action of Ca(2+) that might otherwise occur.

Mechanisms of ion transport inPotamotrygon, a stenohaline freshwater elasmobranch native to the ion-poor blackwaters of the Rio Negro

Stingrays of the family Potamotrygonidae are the only stenohaline freshwater elasmobranchs. Potomotrygon sp. collected from the ion-poor blackwaters ([Na+], [Cl-] and[Ca2+]=10-30 μmol l-1, pH 6.1) of the Rio Negro,Amazonas, Brazil, were ammoniotelic (91% ammonia-N, 9% urea-N excretion) and exhibited blood chemistry (Na+, Cl-, urea, ammonia and glucose levels and osmolality) typical of freshwater teleosts. Unidirectional Na+ and Cl- influx rates, measured with radiotracers,displayed saturation kinetics. The relationships for Cl- and Na+ had similar Km values (300-500 μmol l-1), but Jmax values for Cl-(approximately 950 μmol kg-1 h-1) were almost twice those for Na+ (approximately 500 μmol kg-1h-1). Cl- efflux rates varied with external concentration, but Na+ efflux rates did not. There were no differences in the kinetic variables (Km, Jmax) for influx between animals acclimated to their native ion-poor blackwater or to ion-rich hard water, but efflux rates for both Na+ and Cl- were lower in the former, yielding much lower balance points (external Na+ or Cl- levels at which influx and efflux were equal). Na+, Cl- and Ca2+ uptake were all strongly inhibited by acute exposure to pH 4.0, but efflux rates and Ca2+ binding to the body surface did not change. Na+ influx was inhibited by amiloride (10-4 mol l-1) and by two of its analogs, phenamil (4×10-5mol l-1) and HMA (4×10-5 mol l-1), with the latter being slightly more potent, while Cl- fluxes were unaffected. Cl- fluxes were insensitive to DIDS(2×10-5 mol l-1 or 10-4 mol l-1) and SITS (10-4 mol l-1), but both influx and efflux rates were strongly inhibited by DPC (10-4 mol l-1) and thiocyanate (10-4 mol l-1). Ammonia excretion was unresponsive to large changes in water Na+concentration, but was elevated by 70% during acute exposure to pH 4.0 and transiently inhibited by approximately 50% by amiloride and its analogues. The strategy of adaptation to ion-poor blackwater appears similar to that of some Rio Negro teleosts (Cichlidae) in which low-affinity transport systems are relatively sensitive to inhibition by low pH but are complemented by low diffusive loss rates. Ionic transport systems in these freshwater elasmobranchs, although superficially similar to those in some freshwater teleosts, may bear more resemblance to their presumed evolutionary precursors in marine elasmobranchs.

Diverse strategies for ion regulation in fish collected from the ion-poor, acidic Rio Negro

We measured unidirectional ion fluxes of fish collected directly from the Rio Negro, an extremely dilute, acidic blackwater tributary of the Amazon. Kinetic analysis of Na(+) uptake revealed that most species had fairly similar J(max) values, ranging from 1,150 to 1,750 nmol g(-1) h(-1), while K(m) values varied to a greater extent. Three species had K(m) values <33 micromol L(-1), while the rest had K(m) values >or=110 micromol L(-1). Because of the extremely low Na(+) concentration of Rio Negro water, the differences in K(m) values yield very different rates of Na(+) uptake. However, regardless of the rate of Na(+) uptake, measurements of Na(+) efflux show that Na(+) balance was maintained at very low Na(+) levels (<50 micromol L(-1)) by most species. Unlike other species with high K(m) values, the catfish Corydoras julii maintained high rates of Na(+) uptake in dilute waters by having a J(max) value at least 100% higher than the other species. Corydoras julii also demonstrated the ability to modulate kinetic parameters in response to changes in water chemistry. After 2 wk in 2 mmol L(-1) NaCl, J(max) fell >50%, and K(m) dropped about 70%. The unusual acclimatory drop in K(m) may represent a mechanism to ensure high rates of Na(+) uptake on return to dilute water. As well as being tolerant of extremely dilute waters, Rio Negro fish generally were fairly tolerant of low pH. Still, there were significant differences in sensitivity to pH among the species on the basis of degree of stimulation of Na(+) efflux at low pH. There were also differences in sensitivity to low pH of Na(+) uptake, and two species maintained significant rates of uptake even at pH 3.5. When fish were exposed to low pH in Rio Negro water instead of deionized water (with the same concentrations of major ions), the effects of low pH were reduced. This suggests that high concentrations of dissolved organic molecules in the water, which give it its dark tea color, may interact with the branchial epithelium in some protective manner.

Is breast cancer in young Latinas a different disease?

BACKGROUND

Breast cancer appears to be more aggressive in young women (< or =35 years). Race/ethnicity may further influence prognosis. The purpose of this review is to determine whether breast cancer in young Latinas differs from that in other women.

METHODS

Our institutional (1977-2000) and state (1988-2000) tumor registries were reviewed and breast cancer cases analyzed. Data are expressed as mean +/- SEM.

RESULTS

At our institution, 56 (7%) of 748 breast cancer patients were < or =35 years old; 32 (57%) were Latina. Compared with non-Latinas, Latinas presented at a younger age (P <0.05) and had more stage III/IV disease (38% versus 29%; P >0.05) and bilaterality (22% versus 8%; P >0.05), and worse 5-year survival (63% versus 83%; P >0.05). Statewide data were consistent with our institutional data.

CONCLUSIONS

Latinas comprise a disproportionate share of our young breast cancer population, and may suffer more aggressive disease than other young women. Young Latinas may benefit from more vigilant screening and should be considered for novel therapeutic protocols.

Mesenteric lymph is responsible for post-hemorrhagic shock systemic neutrophil priming

BACKGROUND

Hemorrhagic shock-induced splanchnic hypoperfusion has been implicated as a priming event in the two event model of multiple organ failure (MOF). We have previously shown that early postinjury neutrophil (PMN) priming identifies the injured patient at risk for MOF. Recent in vitro studies have demonstrated that postshock mesenteric lymph primes isolated human neutrophils. We hypothesize that lymphatic diversion before hemorrhagic shock abrogates systemic PMN priming and subsequent lung injury.

METHODS

Sprague-Dawley rats (n >or= 5 per group) underwent hemorrhagic shock (MAP 40 mm Hg x 30 min) and resuscitation (shed blood + 2x crystalloid) with and without mesenteric lymphatic duct diversion. Sham animals underwent anesthesia and laparotomy. Whole blood was taken 2 hours after resuscitation, heparinized, and incubated for 5 min at 37 degrees C. Surface expression of CD11b (a marker for PMN priming) was determined by flow-cytometry compared with isotype controls. In addition, lung myeloperoxidase (MPO) was measured for PMN sequestration, and Evans blue lung leak was assessed in the bronchoalveolar lavage fluid in sham, and shock +/- lymph diversion animals.

RESULTS

Hemorrhagic shock resulted in increased surface expression of PMN CD11b relative to sham (23.8 +/- 6.7 vs. 9.9 +/- 0.6). Mesenteric lymphatic diversion before hemorrhagic shock abrogated this effect (8.0 +/- 2.6). Lung PMN accumulation, as assessed by MPO, was greater in the lungs of nondiverted (113 +/- 14 MPO/mg lung) versus sham (55 +/- 4 MPO/mg lung, p < 0.05); lymph diversion reduced lung PMNs to control levels (71 +/- 6.5 MPO/mg lung, p < 0.05). Evans blue lung leak was 1.6 times sham in the hemorrhagic shock group; this was returned to sham levels after lymph diversion (p < 0.05).

CONCLUSION

Post-hemorrhagic shock mesenteric lymph primes circulating PMNs, promotes lung PMN accumulation, and provokes acute lung injury. Lymphatic diversion abrogates these pathologic events. These observations further implicate the central role of mesenteric lymph in hemorrhagic shock-induced lung injury. Characterizing the PMN priming agents could provide insight into the pathogenesis of postinjury MOF and ultimately new therapeutic strategies.

Hypertonic saline activation of p38 MAPK primes the PMN respiratory burst

Investigation of hypertonic saline (HTS) modulation of neutrophils (PMN) cytotoxic responses has generated seemingly contradictory results. Clinically relevant levels of HTS attenuate receptor-mediated p38 MAPK signaling, whereas higher levels activate p38 MAPK. Concurrently, HTS exerts a dose-dependent attenuation of the PMN respiratory burst, most notably at concentrations where p38 MAPK is activated. We hypothesized that HTS-mediated p38 MAPK activation augments the PMN respiratory burst on return to normotonicity. We found that although clinically relevant levels of HTS (Na+ > or = 200 mM) did not activate p38 MAPK, higher concentrations (Na+ > or = 300 mM) resulted in activation comparable with that after PAF stimulation. Transient stimulation with high levels of HTS primed the PMN respiratory burst in response to fMLP and PMA. This effect was attenuated by pretreatment with SB 203580, a p38 MAPK specific inhibitor. We conclude that severe osmotic shock primes the respiratory burst via p38 MAPK signaling, further supporting the role of this signaling cascade in PMN priming.

Sodium and chloride regulation in freshwater and osmoconforming larvae ofCulexmosquitoes

In this study, we examined aspects of Na+ and Cl– regulation in mosquito larvae of the genus Culex, a group that includes species that tolerate high salinity as well as other forms that are restricted to fresh water. When the euryhaline osmoconformer C. tarsalis was acutely transferred from 30 % to 50 % sea water, the patterns of hemolymph Na+ and Cl– regulation were similar. The underlying regulatory mechanisms for these two ions have very different characteristics. In C. tarsalis, Na+ efflux was significantly elevated compared with the rates measured in the freshwater-restricted C. quinquefasciatus, while Cl– influx was relatively lower. The modulation of Na+ efflux and Cl– influx allowed C. tarsalis to avoid a potential salt load and ionic disturbance in the hemolymph during an acute increase  in salinity. The observed adjustment of NaCl regulation departs from that determined for other euryhaline organisms and is integral to the osmoconforming response. At the other extreme of the salinity spectrum, we observed that C. tarsalis faces difficulties in ion regulation in habitats with low NaCl levels because of its inability to reduce ion efflux and adjust ion absorption rates to maintain hemolymph ion balance. In contrast, C. quinquefasciatus exhibited a reduced ion efflux and the ability to upregulate Na+ uptake, traits necessary to extend its lower salinity limit.

Post-hemorrhagic shock mesenteric lymph lipids prime neutrophils for enhanced cytotoxicity via phospholipase A2

Hemorrhagic shock induced mesenteric hypoperfusion has long been implicated as a key event in the pathogenesis of the adult respiratory distress syndrome (ARDS) and multiple organ failure (MOF). Previous work links post-hemorrhagic shock mesenteric lymph (PHSML) lipids and neutrophil (PMN) priming in the pathogenesis of ARDS. We hypothesize that gut phospholipase A2 (PLA2) liberates proinflammatory lipids following hemorrhagic shock, which are responsible for enhanced PMN cytotoxicity. Mesenteric lymph was collected from rats (n > or = 5) before hemorrhagic shock, during hemorrhagic shock (MAP 40 mm Hg x 30 min), and after resuscitation (shed blood + 2x lactated Ringers). PMNs were incubated with physiologic concentrations (1-5%, v:v) of (a) buffer control, (b) sham (c) pre-shock lymph, (c) PHSML, (d) PHSML lipid extracts, (e) heat-denatured PSHML, and (f) PHSML harvested after i.v. pretreatment with a known PLA2 inhibitor (quinacrine, 10 mg/kg). PMNs were activated with fMLP (1 micromol), and the maximal rate of superoxide production measured by reduction of cytochrome c. Gut morphology was assessed histologically using hematoxalin and eosin (HE) staining. PHSML and PHSML lipid extracts (5%, v:v) primed for enhanced superoxide production compared to buffer controls (2.5-fold and 3.6-fold), sham (2.5-fold) and pre-shock lymph (2.0-fold). Lymph collected after systemic PLA2 inhibition, in contrast, abrogated the PMN priming response. Gut mucosal morphology, at end-resuscitation, was intact on HE staining both with and without PLA2 inhibition. Heat denaturing the PHSML (eliminating cytokines and complement), on the other hand, did not reduce PMN priming. Physiologic concentrations of PHSML lipids prime the PMN respiratory burst. Lymph priming is diminished with systemic PLA2 inhibition, implicating gut PLA2 as a source of proinflammatory lipids that may be central in the pathogenesis of hemorrhagic shock induced ARDS/MOF.

Evaluation of hepatic subcellular fractions for Alamar blue and MTT reductase activity

Alamar blue and MTT are indicators used to measure cytotoxicity of various chemicals in cultured cells. Both Alamar blue and MTT are reduced by mitochondrial enzymes. We observed enhanced fluorescence of Alamar blue when kidney epithelial cells were co-incubated with hepatic post-mitochondrial supernatant (S9) fractions as compared with cells incubated in the absence of S9 fractions. The present studies were carried out to determine whether hepatic cytosolic and/or microsomal enzymes were capable of metabolizing Alamar blue and/or MTT to their reduced products. Livers from female Sprague-Dawley rats were used to prepare S9 fraction, and mitochondrial, microsomal and cytosolic fractions. Fractions containing 1 or 5 mg protein/ml were incubated with Alamar blue or MTT for up to 4 h. Fluorescence (Alamar blue) or absorbance (MTT) were determined and expressed as differences between treated wells and controls. Hepatic fractions (S9, mitochondria, microsomes and cytosol) caused concentration- and time-dependent increases in Alamar blue fluorescence and MTT absorbance. Reduction of Alamar blue and MTT by hepatic S9 fraction was abolished by heating. Reduction of Alamar blue by hepatic mitochondria was approximately equivalent to that catalyzed by hepatic S9 fraction or cytosol. Reduction of MTT by hepatic mitochondria was approximately equivalent to that catalyzed by hepatic S9 fraction or microsomes. These data indicate that mitochondrial, cytosolic and microsomal enzymes reduce Alamar blue and MTT. Therefore, caution should be exercised in ascribing decreases in viability as due solely to mitochondrial damage when using either of these dyes.

Phospholipase A(2)--derived neutral lipids from posthemorrhagic shock mesenteric lymph prime the neutrophil oxidative burst

BACKGROUND

Our previous work identified posthemorrhagic shock mesenteric lymph (PHSML) lipids as key elements in polymorphonuclear neutrophil (PMN)--provoked acute lung injury. We hypothesize that gut phospholipase A(2) (PLA(2)) is responsible for the generation of proinflammatory lipids in PHSML that primes circulating PMNs for enhanced oxidative burst.

METHODS

Mesenteric lymph was collected from rats (n = 5) before (preshock), during the induction of hemorrhagic shock (mean arterial pressure, 40 mm Hg x 30 minutes), and at resuscitation (shed blood + 2x lactated Ringer's solution). PLA(2) inhibition (quinacrine, 10 mg/kg, intravenously) was given before shock was induced. Extracted lipids were separated by normal phase high-pressure liquid chromatography and resuspended in albumin. PMNs were exposed to a 5% vol:vol concentration of eluted lipids and activated with N-formyl-methionyl-leucyl-phenylalanine (1 micromol/L). Superoxide production was assessed by cytochrome C reduction.

RESULTS

High-pressure liquid chromatography--extracted neutral lipids of lymph collected before hemorrhagic shock did not prime the PMN oxidase, whereas isolated neutral lipids of postshock lymph primed PMNs 2.6- +/- 0.32-fold above baseline (P <.05). PLA(2) inhibition returned PHSML neutral lipid priming to baseline levels.

CONCLUSIONS

PLA(2) inhibition before hemorrhagic shock abrogates the neutrophil priming effects of PHSML through reduction of the accumulation of proinflammatory neutral lipids. Identification of these PLA(2)-dependent lipids provides a mechanistic link that may have therapeutic implications for postshock acute lung injury.

Effect of air breathing on acid-base and ion regulation after exhaustive exercise and during low pH exposure in the bowfin, Amia calva

To explore a potential conflict between air breathing and acid-base regulation in the bowfin (Amia calva), we examined how individuals with access to air differed from fish without air access in their response to acidosis. After exhaustive exercise, bowfin with access to air recovered significantly more slowly from the acidosis than fish without air access. While arterial blood pH (pH(a)) of fish without air access recovered to resting levels by 8 h, pH(a) was still significantly depressed in fish having access to air. In addition, Pco(2) was slightly more elevated in fish having air access than those without it. Fish with access to air still had a significant metabolic acid load after 8-h recovery, while those without air access completely cleared the load within 4 h. These results suggest that bowfin with access to air were breathing air and, consequently, were less able to excrete CO(2) and H(+) and experienced a delayed recovery. In contrast, during exposure to low pH, air breathing seemed to have a protective effect on acid-base status in bowfin. During exposure to low pH water, bowfin with access to air developed a much milder acidosis than bowfin without air access. The more severe acidosis in fish without air access was caused by an increased rate of lactic acid production. It appears that enhanced O(2) delivery allowed air-breathing bowfin to avoid acidosis-induced anaerobic metabolism and lactic acid production. In addition, during low pH exposure, plasma Na(+) and Cl(-) concentrations of fish without air access fell slightly more rapidly than those in fish with air access, indicating that the branchial ventilatory changes associated with air breathing limited, to some degree, ion losses associated with low pH exposure.

Evolution of a multidisciplinary clinical pathway for the management of unstable patients with pelvic fractures

OBJECTIVE

To determine whether the evolution of the authors' clinical pathway for the treatment of hemodynamically compromised patients with pelvic fractures was associated with improved patient outcome.

SUMMARY BACKGROUND DATA

Hemodynamically compromised patients with pelvic fractures present a complex challenge. The multidisciplinary trauma team must control hemorrhage, restore hemodynamics, and rapidly identify and treat associated life-threatening injuries. The authors developed a clinical pathway consisting of five primary elements: immediate trauma attending surgeon's presence in the emergency department, early simultaneous transfusion of blood and coagulation factors, prompt diagnosis and management of associated life-threatening injuries, stabilization of the pelvic girdle, and timely insinuation of pelvic angiography and embolization. The addition of two orthopedic pelvic fracture specialists led to a revision of the pathway, emphasizing immediate emergency department presence of the orthopedic trauma attending to provide joint decision making with the trauma surgeon, closing the pelvic volume in the emergency department, and using alternatives to traditional external fixation devices.

METHODS

Using trauma registry and blood bank records, the authors identified pelvic fracture patients receiving blood transfusions in the emergency department. They analyzed patients treated before versus after the May 1998 revision of the clinical pathway.

RESULTS

A higher proportion of patients in the late period had blood pressure less than 90 mmHg (52% vs. 35%). In the late period, diagnostic peritoneal lavage was phased out in favor of torso ultrasound as a primary triage tool, and pelvic binding and C-clamp application largely replaced traditional external fixation devices. The overall death rate decreased from 31% in the early period to 15% in the later period, as did the rate of deaths from exsanguination (9% to 1%), multiple organ failure (12% to 1%), and death within 24 hours (16% to 5%).

CONCLUSIONS

The evolution of a multidisciplinary clinical pathway, coordinating the resources of a level 1 trauma center and directed by joint decision making between trauma surgeons and orthopedic traumatologists, has resulted in improved patient survival. The primary benefits appear to be in reducing early deaths from exsanguination and late deaths from multiple organ failure.

Hypertonic saline attenuation of the neutrophil cytotoxic response is reversed upon restoration of normotonicity and reestablished by repeated hypertonic challenge

BACKGROUND

Hypertonic saline (HTS) resuscitation, in addition to enhancing hemodynamic recovery, modulates postinjury hyperinflammation in the critically injured. The polymorphonuclear neutrophil (PMN) cytotoxic response, a key element in the pathogenesis of postinjury organ dysfunction, is attenuated under hypertonic conditions. Although plasma Na(+) rises to 180 mmol/L after HTS infusion, baseline levels are reestablished within 24 hours. We hypothesized that HTS attenuation of the PMN cytotoxic response (beta2-integrin expression, elastase release, and O2- production) is reversed upon return to normotonicity, but can be reestablished by repeated HTS challenge.

METHODS

Isolated human PMNs were incubated in HTS (Na(+) = 180 mmol/L) for 5 minutes at 37 degrees C then returned to normotonicity by centrifugation and resuspension in isotonic buffer. Stimulated (PAF) beta2-integrin expression was measured by flow cytometry. Stimulated (PAF/fMLP) elastase release and O2- production were measured by cleavage of N-methoxysuccinyl-Ala-Ala-Pro-Val p-nitroanilide and reduction of cytochrome c (Cyt c). Protein tyrosine phosphorylation in PMN cell lysates was assessed by Western blot.

RESULTS

Clinically relevant levels of HTS induced tyrosine phosphorylation in resting PMNs and attenuated cytotoxic responses. Reestablishment of normotonicity returned these functions to baseline. A repeated HTS challenge after restoration of normotonicity also induced tyrosine phosphorylation and suppressed the cytotoxic response.

CONCLUSIONS

HTS attenuation of the PMN cytotoxic response is reversible but can be reestablished by repeated HTS treatment. This phenomenon may provide the unique opportunity to selectively and temporarily decrease the postinjury inflammatory response when patients are at greatest risk for PMN-mediated tissue damage.

Plasma from aged stored red blood cells delays neutrophil apoptosis and primes for cytotoxicity: abrogation by poststorage washing but not prestorage leukoreduction

BACKGROUND

Blood transfusion-particularly that of older stored red blood cells (RBCs)--is an independent risk factor for postinjury multiple organ failure. Immunomodulatory effects of RBC transfusion include neutrophil (PMN) priming for cytotoxicity, an effect exacerbated by longer RBC storage times. We have found that delayed PMN apoptosis in trauma patients is provoked by transfusion, independent of injury severity. We hypothesized that aged stored RBCs delay PMN apoptosis, but that prestorage leukodepletion or poststorage washing could abrogate the effect.

METHODS

Healthy volunteers each donated 1 unit of blood. One half was leukodepleted, and RBC units were processed in the usual fashion and stored at 4 degrees C. Aliquots were removed on days 1, 14, 21, and 42 and the plasma fraction isolated. Selected aliquots were washed with normal saline before plasma isolation. PMNs harvested from healthy controls were incubated (5% CO2, 37 degrees C) with unmodified, leukoreduced, or washed RBC plasma (20% plasma/80% RPMI 1640), and apoptosis assessed by morphology after 24 hours. Apoptotic index (apoptotic PMNs/total PMNs) was compared. PMN priming for superoxide release was also assessed after plasma exposure.

RESULTS

PMN apoptosis was delayed by RBCs stored for 21 or 42 days. Prestorage leukodepletion did not alter the effect. However, washing 42-day-old RBCs abrogated the effect. PMN priming for superoxide was provoked by stored packed RBCs in an identical pattern to delayed apoptosis.

CONCLUSION

Plasma from stored RBCs-even if leukoreduced-delays apoptosis and primes PMNs. The effect becomes evident at 21 days and worsens through product outdate (42 days), but may be prevented by poststorage washing. Inflammatory agents contaminating stored blood likely mediate the effect. Modification of transfusion practices (e.g., giving fresher or washed RBCs or blood substitutes) may attenuate adverse immunomodulatory effects of transfusion in trauma patients.

The lipid fraction of post-hemorrhagic shock mesenteric lymph (PHSML) inhibits neutrophil apoptosis and enhances cytotoxic potential

Dysfunctional neutrophil (PMN) apoptosis facilitates hyperinflammatory tissue injury. Previous work has demonstrated that post-hemorrhagic shock mesenteric lymph (PHSML) provokes PMN-mediated acute lung injury in animal models, but the mechanism remains unclear. We have documented that the lipid fraction of PHSML is responsible for PMN priming of the respiratory burst. In this study, we hypothesized that PHSML lipids delay PMN apoptosis and thereby further enhance PMN cytotoxic potential. Mesenteric lymph was collected from rats (n = 5) before (control), during non-lethal hemorrhagic shock (MAP 40 mmHg, 30 min), and during resuscitation (shed blood + 2x crystalloid). Human PMNs were incubated with control, PHSML, PHSML lipid extracts, and heat-treated PHSML (60 degrees C, 30 min.) at 1-10% (v:v) in RPMI 1640 for 24 h. Apoptosis was assessed using acridine orange/ethidium bromide staining and fluorescence microscopy. Priming of the respiratory burst was evaluated by incubating PMNs with (a) control PHSML or (b) PHSML lipid extracts for 24 h and by activating with fMLP (1 micromol/L). PHSML and PHSML lipid extracts (5-10%) inhibited PMN apoptosis. Heat denaturing the PHSML (to eliminate cytokines and complement) had no effect on the inhibition of PMN apoptosis. Similarly, incubation with polymixin B at a concentration that binds endotoxin had no effect. Both the PHSML and PHSML lipids (5%) following 24-h incubation primed the fMLP-activated oxidase. At physiologic concentrations, both PHSML and the lipid fraction of PHSML delay PMN apoptosis and prime the NADPH oxidase. These data further implicate the lipid components of mesenteric lymph as central in the pathogenesis of hemorrhagic shock induced PMN-mediated acute lung injury.

Hypertonic saline inhibits neutrophil (PMN) priming via attenuation of p38 MAPK signaling

Priming of the neutrophil cytotoxic response is central to the pathogenesis of early postinjury multiple organ failure (MOF). Platelet-activating factor (PAF) has been implicated as a key inflammatory mediator in postinjury neutrophil priming and requires p38 MAPK signaling to produce its biologic effects. Hypertonic saline (HTS) resuscitation decreases the postinjury inflammatory response following shock in animals and decreases receptor-mediated neutrophil (PMN) cytotoxic functions in vitro. We hypothesized that HTS attenuates PAF priming of the PMN cytotoxic response by interfering with PAF-mediated p38 MAPK signal transduction. Isolated PMNs were preincubated in isotonic buffer or HTS (Na+ = 180 mM), then primed with PAF. Neutrophil CD11b/CD18 expression was measured by flow cytometry. Receptor-dependent (fMLP), N-formyl-methionyl-leucyl-phenylalanine, fMLP) and receptor-independent (PMA) O2- production was measured by reduction of cytochrome c in resting and PAF primed PMNs. Total p38 MAPK protein PAF-mediated p38 MAPK activation was assessed by western blot of PMN lysates. Clinically relevant levels of HTS attenuated PAF-mediated beta2-integrin expression. While HTS attenuated receptor-dependent (fMLP and PAF/fMLP) O2- production, receptor-independent (PMA) O2- production was unaffected. Conversely, HTS attenuated PAF priming of PMA-mediated O2- production. PAF and HTS did not alter total cellular p38 MAPK content. Clinically relevant levels of HTS alone did not activate p38 MAPK but inhibited PAF mediated p38 MAPK activation. HTS attenuates PAF priming of the PMN cytotoxic response by altering intracellular signal transduction. Therefore, HTS resuscitation may attenuate postinjury PMN priming and ultimately the risk of developing MOF.

Ion and acid-base balance in three species of Amazonian fish during gradual acidification of extremely soft water

Sensitivity to acid water was assessed in three species of Amazonian fish that encounter naturally acidic blackwaters to differing degrees in the wild: tambaqui (Colossoma macropomum), matrincha (Brycon erythropterum), and tamoatá (Hoplosternum littorale), in decreasing order of occurrence in blackwater. Fish were exposed to a graded reduction in water pH, from pH 6 to 5 to 4 to 3.5, followed by return to pH 6. Fish were exposed to each new pH for 24 h. During these exposures, net transfers of ions (Na+, K+, Cl-, and Ca2+) and acid-base equivalents to and from the external water were used as physiological indicators of acid tolerance. Exposure to pH 5 had a minimal effect on net ion fluxes. Significant net losses of all ions (except Ca2+) were recorded in all three species during the first few hours of exposure to pH 4. However, ion balance was usually restored within 18 h at pH 4. Exposure to pH 3.5 caused even greater ion losses in all three species and proved to be acutely lethal to tamoatá. Matrincha sustained irreversible physiological damage at pH 3.5, as ion fluxes did not recover following return to pH 6 and there was some mortality. Tambaqui suffered the least ionoregulatory disturbances at pH 3.5 and was the only species to make a full recovery on return to pH 6. In all species, there was a tendency for ammonia excretion to increase at low water pH, but even at pH 3.5, there was no significant net uptake of acid from the water. Overall, there was a strong relationship between the magnitude of ionic disturbances and the lethality of exposure to low pH. The relative insensitivity of the ionoregulatory system of tambaqui to low pH indicates that this is a feature of fish native to blackwater systems rather than one that is common to all Amazon fish.

Ionoregulatory specializations for exceptional tolerance of ion-poor, acidic waters in the neon tetra (Paracheirodon innesi)

To better understand how fish are able to inhabit dilute waters of low pH, we examined ionoregulation in exceptionally acid-tolerant neon tetras (Paracheirodon innesi), which are native to the ion-poor, acidic Rio Negro, Amazon. Overall ion balance was unaffected by 2-wk exposure to pH 4.0 and 3.5. Measurements of unidirectional Na+ fluxes during exposure to pH 3.5 showed that tetras experienced only a mild, ionic disturbance of short duration (</=24 h) as a result of a stimulation of Na+ efflux. At pH 3.25, Na+ efflux was almost fourfold greater (all fish died within 6-8 h). At both pHs, active Na+ uptake was not inhibited, and in fact, at pH 3.5, uptake was stimulated. Kinetic analysis of Na+ uptake at pH 6.5 and 3.5 produced virtually identical low Km values and high maximum-transport values. These results confirmed the pH insensitivity of the uptake mechanism and revealed a mechanism well designed to operate in the dilute, acidic waters of the Rio Negro. Na+ influx was only mildly sensitive to amiloride (a Na+ channel blocker), which, along with the pH insensitivity, suggests that Na+ uptake may occur by a novel mechanism. Na+ efflux was reduced by addition of Ca2+ to the test water at pH 6.5, but the effect disappeared at pH 3.5. Exposure to LaCl3 (a strong Ca2+ displacer) also stimulated Na+ efflux. These results suggest that Ca2+ plays a role in determining branchial ion permeability at high pH but that, at low pH, where Na+ efflux is stimulated, alternate, Ca2+-independent mechanisms are employed to control Na+ efflux.

Responses of an Amazonian teleost, the tambaqui (Colossoma macropomum), to low pH in extremely soft water

Our goal was to compare the internal physiological responses to acid challenge in an acidophilic tropical teleost endemic to dilute low-pH waters with those in nonacidophilic temperate species such as salmonids, which have been the subjects of most previous investigations. The Amazonian tambaqui (Colossoma macropomum), which migrates between circumneutral water and dilute acidic "blackwater" of the Rio Negro, was exposed to a graded low-pH and recovery regime in representative soft water (Na+ = 15, Cl- = 16, Ca2+ = 20 mumol L-1). Fish were fitted with arterial catheters for repetitive blood sampling. Water pH was altered from 6.5 (control) to 5.0, 4.0, 3.0, and back to 6.5 (recovery) on successive days. Some deaths occurred at pH 3.0. Throughout the regime, there were no disturbances of blood gases (O2 and CO2 tensions and contents) or lactate levels, and only very minor changes in acid-base status of plasma and red cells. However, erythrocytic guanylate and adenylate levels increased at pH's less than or equal to 5.0. Down to pH 4.0, plasma glucose, cortisol, and total ammonia levels remained constant, but all increased at pH 3.0, denoting a stress response. Plasma Na+ and Cl- levels declined and plasma protein concentration increased at pH 3.0, indicative of ionoregulatory and fluid volume disturbance, and neither recovered upon return to pH 6.5. Cortisol and ammonia elevations also persisted. Transepithelial potential changed progressively from highly negative values (inside) at pH 6.5 to highly positive values at pH 3.0; these alterations were fully reversible. Experimental elevations in water calcium levels drove the transepithelial potential positive at circumneutral pH, attenuated or prevented changes in transepithelial potential at low pH, and reduced Na+ and Cl- loss rates to the water during acute low-pH challenges. In general, tambaqui exhibited responses to low pH that were qualitatively similar but quantitatively more resistant than those previously documented in salmonids.

Effects of water pH and calcium concentration on ion balance in fish of the Rio Negro, Amazon

We examined the effects of acute low-pH exposure on ion balance (Na+, Cl-, K+) in several species of fish captured from the Rio Negro, a dilute, acidic tributary of the Amazon. At pH 5.5 (untreated Rio Negro water), the four Rio Negro species tested (piranha preta, Serrasalmus rhombeus; piranha branca, Serrasalmus cf. holandi; aracu, Leporinus fasciatus; and pacu, Myleus sp.) were at or near ion balance; upon exposure to pH 3.5, while Na+ and Cl- loss rates became significant, they were relatively mild. In comparison, tambaqui (Colossoma macropomum), which were obtained from aquaculture and held and tested under the same conditions as the other fish, had loss rates seven times higher than all the Rio Negro species. At pH 3.0, rates of Na+ and Cl- loss for the Rio Negro fish increased three- to fivefold but were again much less than those observed in tambaqui. Raising water Ca2+ concentration from 10 micromol L-1 to 100 micromol L-1 during exposure to the same low pH's had no effect on rates of ion loss in the three species tested (piranha preta, piranha branca, aracu), which suggests that either they have such a high branchial affinity for Ca2+ that all sites are saturated at 10 micromol L-1 and additional Ca2+ had no effect, or that Ca2+ may not be involved in regulation of branchial ion permeability. For a final Rio Negro species, the cardinal tetra (Paracheirodon axelrodi), we monitored body Na+ concentration during 5 d of exposure to pH 6.0, 4.0, or 3.5. These pH's had no effect on body Na+ concentration. These data together suggest that exceptional acid tolerance is a general characteristic of fish that inhabit the dilute acidic Rio Negro and raise questions about the role of Ca2+ in regulation of branchial ion permeability in these fish.

Cytologic evaluation of lumpectomy margins in patients with ductal carcinoma in situ: clinical outcome

BACKGROUND

Breast conservation therapy is controversial for ductal carcinoma in situ (DCIS) due to recently reported high recurrence rates. We believe that cytologic evaluation of lumpectomy margins improves efficiency and leads to a lower recurrence rate following lumpectomy for DCIS.

METHODS

A prospectively accrued database of 1255 breast cancer patients at the H. Lee Moffitt Cancer Center and Research Institute was found to have 218 patients with DCIS (17.4%). Of those 218 cases, 114 were treated with lumpectomy, axillary dissection, and radiation therapy; the remaining 104 patients were treated with mastectomy with or without reconstruction. Imprint cytology was used to evaluate all lumpectomy margins. Permanent sections and imprint cytology were reviewed by the same pathologist.

RESULTS

All lumpectomy specimens (116 tumors in 114 patients) were evaluated. The median follow up was 57.5 months (range 2-110 months). One hundred and three patients with 104 tumors were selected on the basis of pure DCIS (with or without microinvasion), and treated with lumpectomy, axillary dissection and radiation therapy. Of the 104 tumors utilizing attempted breast conservation therapy, 7 (6.6%) required mastectomy. There were 6 recurrences (6.1%) with a median time for recurrence of 47.5 months (range 27-85 months); four recurrences were comedo and two were noncomedo at original diagnosis.

CONCLUSIONS

The determination of lumpectomy margins in DCIS patients using imprint cytology leads to an overall recurrence rate of 6.1% with reduction in operative time, and re-excision rate. Significant recurrence rates were associated with microinvasion and multifocal tumors (28%) versus simple DCIS at 5 years. Breast conservation therapy and surgical margin determination with imprint cytology for DCIS is a cost-effective and reliable method of treatment for simple DCIS.

Ion regulation in ion-poor acidic water by the blackskirt tetra (Gymnocorymbus ternetzi), a fish native to the Amazon River

We examined the ionoregulatory capabilities of the blackskirt tetra (Gymnocorymbus ternetzi), which is native to ion-poor acidic waters of the Amazon River. Examination of Na+ uptake, which was only slightly sensitive to the uptake blocker amiloride, revealed several specializations for uptake in these waters. Kinetic analysis of Na+ uptake (at pH 6.5) revealed a high maximum rate of uptake and a low Michaelis-Menten constant, which allows the tetras to take up Na+ at high rates even at very low water levels. At pH 4.5, a pH where they experience sizable ion disturbances, they displayed several mechanisms to restore balance. Kinetic analysis at pH 4.5 revealed that the maximum uptake rate rose 67% while the Michaelis-Menten constant remained unchanged. Further tests showed that the upregulation of Na+ uptake occurred within 12 h in response to a doubling of Na+ efflux. Despite these specializations of the Na+ uptake mechanism, blackskirt tetras were not especially tolerant of low pH. Upon exposure to pH 4.0, they experienced a massive loss of Na+ due to a fourfold increase of Na+ efflux (relative to pH 5.0) and an 80% inhibition of uptake. Measurement of Na+ efflux in waters with different Ca2+ levels and in the presence of LaCl, a strong Ca2+ competitor, correlated the stimulation of Na+ efflux at low pH with a low branchial affinity for Ca2+. These tests indicate that blackskirt tetras possess abilities to resist the disruptive effects of moderately low pH but cannot survive in waters with a pH of 4.0 or less because of leaching of Ca2+ from branchial tight junctions, which stimulates ion losses.

Bulk flow of the medium and cutaneous sodium uptake in frogs: potential significance of sodium and oxygen boundary layers

To examine the potential impact of fluid dynamic boundary layers on cutaneous ion exchange, we investigated how bulk flow of dilute Na+ solutions (&lt; or = 1.0 mmol l-1) over the skin of intact frogs (Rana catesbeiana and Rana pipiens) affects cutaneous Na+ uptake (JNa(in)) and transepithelial potential (TEP). Cessation of stirring resulted in a 14-35% decrease in TEP and a 14-65% decrease in JNa(in). Two weeks' acclimation to an unstirred bath increased JNa(in) to levels 70% greater than in frogs acclimated to a continuously stirred bath and to levels comparable to those of frogs acclimated to deionized water. These effects are consistent with depletion of Na+ in the boundary layer, but are also consistent with depletion of O2 in the boundary layer, which might limit generation of ATP consumed by ATPases responsible for cutaneous Na+ uptake. To investigate this latter possibility, we measured TEP and JNa(in) while manipulating the PO2 of well-stirred external media at constant [Na+]. Hyperoxia (PO2 &gt; or = 97 kPa) increased JNa(in) by 28% and had little or no effect on TEP. Hypoxia (PO2 &lt; or = 1.5 kPa) reduced JNa(in) by 48% and decreased TEP by 22%. These results suggest that ionic and gaseous boundary layers may interact to affect cutaneous ion transport.