The role of the skin microbiota in acne pathophysiology

BACKGROUND

The role of skin microbiota in acne remains to be fully elucidated. Initial culture-based investigations were hampered by growth rate and selective media bias. Even with less biased genomic methods, sampling, lysis and methodology, the task of describing acne pathophysiology remains challenging. Acne occurs in sites dominated by Cutibacterium acnes (formerly Propionibacterium acnes) and Malassezia species, both of which can function either as commensal or pathogen.

OBJECTIVES

This article aims to review the current state of the art of the microbiome and acne.

METHODS

The literature regarding the microbiome and acne was reviewed.

RESULTS

It remains unclear whether there is a quantitative difference in microbial community distribution, making it challenging to understand any community shift from commensal to pathogenic nature. It is plausible that acne involves (i) change in the distribution of species/strains, (ii) stable distribution with pathogenic alteration in response to internal (intermicrobe) or external stimuli (host physiology or environmental) or (iii) a combination of these factors.

CONCLUSIONS

Understanding physiological changes in bacterial species and strains will be required to define their specific roles, and identify any potential intervention points, in acne pathogenesis and treatment. It will also be necessary to determine whether any fungal species are involved, and establish whether they play a significant role. Further investigation using robust, modern analytic tools in longitudinal studies with a large number of participants, may make it possible to determine whether the microbiota plays a causal role, is primarily involved in exacerbation, or is merely a bystander. It is likely that the final outcome will show that acne is the result of complex microbe-microbe and community-host interplay.

What women want - quantifying the perception of hair amount: an analysis of hair diameter and density changes with age in caucasian women

BACKGROUND

It has long been known that women lose satisfaction with their hair with ageing. Our data show that caucasian women perceive a decrease in hair amount in their mid 40s with a further decrease in the mid to late 50s, which leads to this dissatisfaction. Neither loss of density (hairs per cm(2) ) nor shaft diameter alone can fully account for this perception. A new metric, 'hair amount', is proposed as a quantitative metric combining the impact of both density and diameter on the perception of hair loss.

OBJECTIVES

Creation of a single parameter combining the contribution of diameter and density to perception of female age-related hair loss.

METHODS

In total, 1099 caucasian women (ages 18-66 years) with self-perceived hair loss and 315 caucasian women (ages 17-86 years) with no complaint of hair loss were evaluated. Scalp hair diameter was measured using optical fibre diameter and image analysis. Scalp hair density was measured by phototrichogram with manual or automated counting.

RESULTS

Parietal scalp hair diameter increased from ages 20 to 40-45 years, then decreased. Hair density was highest in the youngest group, age 20-30 years, and decreased thereafter with increasing rate. In women self-perceiving hair loss, the rate of decrease in density was significantly faster than for women with no self-perception of hair loss. The combined metric 'hair amount' was relatively constant at younger ages, increasing very slightly to age 35 years, then decreasing significantly.

CONCLUSIONS

Increasing hair shaft diameter offsets decreasing hair density through the mid 30s. After that, a lower rate of diameter increase combined with the decrease in density begins to significantly impact the perception of hair amount so that thinning becomes increasingly more noticeable in the mid 40s to the mid to late 50s. Quantitative determination of hair amount is a useful tool to combine the contributions of hair density and diameter to women's perception of age-related hair loss.

Hair loss in women: medical and cosmetic approaches to increase scalp hair fullness

Androgenetic alopecia affects both men and women. In men it produces male pattern hair loss with bitemporal recession and vertex baldness. In women it produces female pattern hair loss (FPHL) with diffuse alopecia over the mid-frontal scalp. FPHL occurs as a result of nonuniform hair follicle miniaturization within follicular units. Diffuse alopecia is produced by a reduction in the number of terminal fibres per follicular unit. Baldness occurs only when all hairs within the follicular units are miniaturized and is a relatively late event in women. The concepts of follicular units and primary and secondary hair follicles within follicular units are well established in comparative mammalian studies, particularly in sheep. However, discovery of these structures in the human scalp hair and investigation of the changes in follicular unit anatomy during the development of androgenetic alopecia have provided a clearer understanding of the early stages of androgenetic alopecia and how the male and female patterns of hair loss are related. FPHL is the most common cause of alopecia in women and approximately one-third of adult caucasian women experience hair loss. The impact of FPHL is predominantly psychological. While men anticipate age-related hair loss, hair loss in women is usually unexpected and unwelcome at any age. Treatment options to arrest hair loss progression and stimulate partial hair regrowth for FPHL include the androgen receptor antagonists spironolactone and cyproterone acetate, the 5α-reductase inhibitor finasteride and the androgen-independent hair growth stimulator minoxidil. These treatments appear to work best when initiated early. Hair transplantation should be considered in advanced FPHL that is resistant to medical treatments. Hair transplantation requires well-preserved hair growth over the occipital donor area. The psychological impact of FPHL may also be reduced by cosmetic products that improve the appearance of the hair. These agents work to minimize hair fibre breakage, improve hair volume or conceal visible bald scalp.

A novel cosmetic approach to treat thinning hair

BACKGROUND

Many of today's treatments associated with 'thinning hair', such as female pattern hair loss and telogen effluvium, are focused on two of the key aspects of the condition. Over-the-counter or prescription medications are often focused on improving scalp hair density while high-quality cosmetic products work to prevent further hair damage and minimize mid-fibre breakage. Fibre diameter is another key contributor to thinning hair, but it is less often the focus of medical or cosmetic treatments.

OBJECTIVES

To examine the ability of a novel leave-on technology combination [caffeine, niacinamide, panthenol, dimethicone and an acrylate polymer (CNPDA)] to affect the diameter and behaviour of individual terminal scalp hair fibres as a new approach to counteract decreasing fibre diameters.

METHODS

Testing methodology included fibre diameter measures via laser scan micrometer, assessment of fibre mechanical and behavioural properties via tensile break stress and torsion pendulum testing, and mechanistic studies including cryoscanning electron microscopy and autoradiographic analysis.

RESULTS

CNPDA significantly increased the diameter of individual, existing terminal scalp hair fibres by 2-5 μm, which yields an increase in the cross-sectional area of approximately 10%. Beyond the diameter increase, the CNPDA-thickened fibres demonstrated the altered mechanical properties characteristic of thicker fibres: increased suppleness/pliability (decreased shear modulus) and better ability to withstand force without breaking (increased break stress).

CONCLUSIONS

Although cosmetic treatments will not reverse the condition, this new approach may help to mitigate the effects of thinning hair.

It must be green: meeting society’s environmental concerns

Consumers today are increasingly demanding goods which not only conform to the public’s image of being ‘eco‐friendly’ and ‘organic’ but of having been produced ‘ethically’. Meeting such high ideals has a down side, both in higher costs and often in that of having to accept more distant suppliers. Present trends in the coloration of foods with natural dyes rather than synthetic ones, increasing consumption of organic products (including fibres) and energy‐saving trends in dye application methods, fuels and lighting, as well as the means of capturing solar energy, are discussed. The discovery of some interesting and historic green colours, the wider use of green (in both senses of the word) products and green chemistry’s future role in producing them are also reviewed.

Moral and evaluative reasoning across the life-span

In a longitudinal/cross sectional study of moral and evaluative reasoning, Armon interviewed 23 females and 19 males, ages ranging from 5 at the first test time (1977) to 86 at the 4th (1989) test-time. Rasch analysis of Armon's data demonstrated that Armon's and Kohlberg's measures tap a single underlying dimension of reasoning; that individual stages across five items measure the same levels of reasoning, and that development on all items progresses at about the same rate. Participants found it easier to apply already available reasoning structures to new areas than to reason at a new stage, implying that stage transition is step-like.

Dandruff has an altered stratum corneum ultrastructure that is improved with zinc pyrithione shampoo

Transmission electron microscopy of scalp tape strips indicates that dandruff scalp possesses abnormal stratum corneum (SC) ultrastructure that is normalized by treatment with small-particle zinc pyrithione (ZPT). Similar abnormalities occur throughout the scalp of those with dandruff, even where no flaking is present. SC abnormalities are consistent with hyperproliferation, including parakeratosis, lipid droplets within corneocytes, few desmosomes, corneocyte membrane interdigitation, and excessive disorganized intercellular lipid. Reversal of SC abnormalities would require treatment of the cause(s) of dandruff, not merely flake removal. A protocol was developed to quantify scalp structural abnormalities by scoring cells from scalp tape strips for yeast number, amount of intercellular lipid, normal intercellular lipid structures, prevalence of intracellular lipid droplets, parakeratotic corneocytes, and corneocyte interdigitation. This protocol was used to compare dandruff and normal SC to dandruff SC treated with either commercial ZPT-containing shampoo or a placebo. Treatment with commercial ZPT shampoo significantly returned SC ultrastructure to normal, suggesting control of the cause of dandruff.

Systemic correction of the muscle disorder glycogen storage disease type II after hepatic targeting of a modified adenovirus vector encoding human acid-alpha-glucosidase

This report demonstrates that a single intravenous administration of a gene therapy vector can potentially result in the correction of all affected muscles in a mouse model of a human genetic muscle disease. These results were achieved by capitalizing both on the positive attributes of modified adenovirus-based vectoring systems and receptor-mediated lysosomal targeting of enzymes. The muscle disease treated, glycogen storage disease type II, is a lysosomal storage disorder that manifests as a progressive myopathy, secondary to massive glycogen accumulations in the skeletal and/or cardiac muscles of affected individuals. We demonstrated that a single intravenous administration of a modified Ad vector encoding human acid alpha-glucosidase (GAA) resulted in efficient hepatic transduction and secretion of high levels of the precursor GAA proenzyme into the plasma of treated animals. Subsequently, systemic distribution and uptake of the proenzyme into the skeletal and cardiac muscles of the GAA-knockout mouse was confirmed. As a result, systemic decreases (and correction) of the glycogen accumulations in a variety of muscle tissues was demonstrated. This model can potentially be expanded to include the treatment of other lysosomal enzyme disorders. Lessons learned from systemic genetic therapy of muscle disorders also should have implications for other muscle diseases, such as the muscular dystrophies.

Isolation and nucleotide sequence of human liver glycogen debranching enzyme mRNA: identification of multiple tissue-specific isoforms

Glycogen storage disease type III (GSD-III) is caused by a deficiency of glycogen debranching enzyme (AGL) activity. Patients are found to have deficient AGL activity in both muscle and liver, and also enzyme deficiency in the liver, but not in muscle. To determine the molecular basis of enzymatic variability in GSD-III and to elucidate the mechanism for control of tissue-specific expression of AGL, we previously cloned and sequenced the human muscle AGL cDNA. Here we report the isolation and nucleotide sequence of liver AGL cDNA and the tissue distribution of the isoform mRNAs. The predominant form of human liver AGL cDNA (isoform 1) contained 400 bp of 5' untranslated region, 4596 bp of coding region, and 2371 bp of 3' untranslated region. The liver AGL mRNA sequence was identical to the previously published muscle sequence (isoform 5) for most of the length, except for the 5' end, in which the liver sequence diverged completely from the muscle sequence. The divergence began with the transcription start point and extended 82 nucleotides downstream from the translation initiation codon. Six isoforms of AGL mRNA were identified and sequenced from liver and muscle. These isoforms differed only at the 5' end. Tissue distribution studies showed that liver, kidney and lymphoblastoid cells expressed predominantly isoform 1; whereas muscle and heart expressed not only isoform 1, but also muscle-specific isoform mRNAs (isoforms 2, 3 and 4). Defining tissue-specific AGL isoform mRNAs is an important step toward understanding the molecular basis of enzymatic variability in GSD-III.

Human glycogen debranching enzyme gene (AGL): complete structural organization and characterization of the 5' flanking region

Glycogen debranching enzyme (gene symbol, AGL) is a multifunctional enzyme acting as 1,4-alpha-D-glucan:1,4-alpha-D-glucan 4-alpha-D-glycosyltransferase and amylo-1,6-glucosidase in glycogen degradation. Genetic deficiency of AGL activity causes glycogen storage disease type III (GSD-III). To determine the molecular basis of GSD-III and elucidate the mechanisms for controlling tissue-specific gene expression, we report the isolation and structural organization of the human chromosomal AGL gene. The gene is 85 kb in length and is composed of 35 exons, encoding a 7.0-kb mRNA. The first 2 exons and 68 bp of exon 3 contain 5' untranslated region. Translation begins in exon 3, which encodes the first 27 amino acids of the AGL. Exons 4 to 35 encode the remaining 1505 amino acids. Among the 6 isoforms identified, the major isoform (isoform 1) starts with exon 1 and is widely expressed, including expression in both liver and muscle. Muscle-specific isoforms (2, 3, and 4) begin with exon 2. Isoforms 5 and 6 are minor isoforms that begin further within the gene. Reporter assays revealed that promoter region 1 (for isoform 1) was functional in liver (HepG2 cells), muscle (C2C12 cells), and ovary (Chinese hamster ovary cells), and promoter region 2 (for muscle-specific isoforms) was active only in muscle. These results suggest that the human AGL gene contains at least 2 promoter regions that confer differential expression of isoform mRNAs in a tissue-specific manner.

Activation of a novel calcium-dependent protein-tyrosine kinase. Correlation with c-Jun N-terminal kinase but not mitogen-activated protein kinase activation

Many G protein-coupled receptors (e.g. that of angiotensin II) activate phospholipase Cbeta, initially increasing intracellular calcium and activating protein kinase C. In the WB and GN4 rat liver epithelial cell lines, agonist-induced calcium signals also stimulate tyrosine phosphorylation and subsequently increase the activity of c-Jun N-terminal kinase (JNK). We have now purified the major calcium-dependent tyrosine kinase (CADTK), and by peptide and nucleic acid sequencing identified it as a rat homologue of human PYK2. CADTK/PYK2 is most closely related to p125(FAK) and both enzymes are expressed in WB and GN4 cells. Angiotensin II, which only slightly increases p125(FAK) tyrosine phosphorylation in GN4 cells, substantially increased CADTK tyrosine autophosphorylation and kinase activity. Agonists for other G protein-coupled receptors (e.g. LPA), or those increasing intracellular calcium (thapsigargin), also stimulated CADTK. In comparing the two rat liver cell lines, GN4 cells exhibited approximately 5-fold greater angiotensin II- and thapsigargin-dependent CADTK activation than WB cells. Although maximal JNK activation by stress-dependent pathways (e.g. UV and anisomycin) was equivalent in the two cell lines, calcium-dependent JNK activation was 5-fold greater in GN4, correlating with CADTK activation. In contrast to JNK, the thapsigargin-dependent calcium signal did not activate mitogen-activated protein kinase and Ang II-dependent mitogen-activated protein kinase activation was not correlated with CADTK activation. Finally, while some stress-dependent activators of the JNK pathway (NaCl and sorbitol) stimulated CADTK, others (anisomycin, UV, and TNFalpha) did not. In summary, cells expressing CADTK/PYK2 appear to have two alternative JNK activation pathways: one stress-activated and the other calcium-dependent.

Angiotensin II activates at least two tyrosine kinases in rat liver epithelial cells. Separation of the major calcium-regulated tyrosine kinase from p125FAK

In rat liver epithelial cell lines (WB or GN4), angiotensin II (Ang II) stimulates cytosolic tyrosine kinase activity, in part, through a calcium-dependent mechanism. In other cell types, selected hormones that activate Gi- or Gq-coupled receptors stimulate the soluble tyrosine kinase, p125FAK. Immunoprecipitation of p125FAK from Ang II-activated GN4 cells demonstrated a doubling of p125FAK kinase activity. However, an additional Ang II-activated tyrosine kinase (or kinases) representing the majority of the total activity was detected when the remaining cell lysate, immunodepleted of p125FAK, was reimmunoprecipitated with an anti-phosphotyrosine antibody. Cytochalasin D pretreatment blocks G-protein receptor-dependent tyrosine phosphorylation in Swiss 3T3 cells. While cytochalasin D decreased the Tyr(P) content of 65-75-kDa substrates in Ang II-treated GN4 cells, it did not diminish tyrosine phosphorylation of 115-130-kDa substrates, again suggesting activation of at least two tyrosine kinase pathways in GN4 cells. To search for additional Ang II-activated enzymes, we used molecular techniques to identify 20 tyrosine kinase sequences in these cell lines. None was the major cytosolic enzyme activated by Ang II. Specifically, JAK2, which had been shown by others to be stimulated by Ang II in smooth muscle cells, was not activated by Ang II in GN4 cells. Finally, we purified Tyr(P)-containing tyrosine kinases from Ang II-treated cells, using anti-Tyr(P) and ATP affinity resins; 80% of the tyrosine kinase activity migrated as a single 115-120-kDa tyrosine-phosphorylated protein immunologically distinct from p125FAK. In summary, Ang II activates at least two separate tyrosine kinases in rat liver epithelial cells; p125FAK and a presumably novel, cytosolic 115-120-kDa protein referred to as the calcium-dependent tyrosine kinase.

Heterodimerization and functional interaction between EGF receptor family members: a new signaling paradigm with implications for breast cancer research

The EGF receptor (EGFR) and HER2 are members of a growth factor receptor family. Overexpression of either protein in advanced breast cancer correlates with poor prognosis. EGF stimulates growth by binding to EGFR, activating the receptor's intracellular tyrosine kinase. The initial consequence is phosphorylation of specific tyrosine-containing sequences in the receptor's carboxyl terminus. These phosphotyrosines serves as high affinity recognition sites for proteins that, in turn, transmit the growth signal inside the cell. Mechanistic studies suggest that EGF binds to a single EGFR, triggering dimerization with another like receptor molecule. This dimerization is thought to initiate the tyrosine kinase activation. The EGF receptor family was recently expanded with the sequencing of HER3 and HER4. Each of the four family members was postulated to regulate a unique growth or differentiation signaling repertoire when activated by a receptor-specific ligand. However, new data from numerous laboratories suggest that EGFR family members may play a complex and ultimately more flexible role in signaling by forming heterodimers between family members, e.g. EGFR:HER2 or HER4:HER2. These heterodimers may form even when only one member of the pair binds its ligand. This review summarizes current work on heterodimerization and attempts to predict the consequences for downstream signaling. In brief, when compared to ligand-dependent receptor homodimers comprised of two proteins with the same internalization sequence and phosphorylated tyrosine residues, heterodimers are likely to: i) expand substrate selection and downstream signaling pathway activation; ii) promote interaction between sets of substrates in the mixed receptor complexes that would not ordinarily be physically juxtaposed; iii) alter the duration of receptor signaling by changing rates of receptor internalization, ligand loss, kinase inactivation, recycling, etc.; and iv) alter rates of receptor and substrate dephosphorylation. In addition to understanding interactions of heterodimers with the internalization machinery, identification of receptor-specific substrates and binding proteins for each EGFR family member will be necessary to explicate the role of heterodimers in growth and differentiation.

Cloning and developmental expression analysis of the murine c-mer tyrosine kinase

We have cloned the putative mouse homologue of the human c-mer receptor tyrosine kinase proto-oncogene. Comparison of the mouse and human c-mer amino acid sequences reveals an overall identity of 88%. Similar to the human, the extracellular region of the murine c-mer protein possesses two amino terminal immunoglobulin-like domains and two membrane proximal fibronectin type III domains, which places it in the Axl family of tyrosine kinases. Our analysis of the Axl family identifies eight different regions of amino acid consensus that have residues characteristic of this and no other tyrosine kinase family; six of the eight are within tyrosine kinase subdomains. The homology within the Axl family is highest between c-mer and c-eyk, the chicken proto-oncogene of the tumor virus gene product v-eyk. Northern analysis of adult tissues suggests that the mouse c-mer, although expressed in many tissues, has an expression pattern unique among Axl family members. In normal adult hematopoietic cells c-mer seems to be expressed predominantly if not exclusively in the monocytic lineage. Mouse c-mer is expressed during most, if not all, stages of embryological development beginning in the morula and blastocyst and progressing through the yolk sac and fetal liver stages. This early and consistent expression of c-mer was confirmed during in vitro differentiation of embryonic stem cells. The embryonic expression profile of c-mer suggests that this tyrosine kinase may play an important function in the developing mouse.

Cloning and mRNA expression analysis of a novel human protooncogene, c-mer

A human B-lymphoblastoid lambda gt11 expression library was screened using anti-phosphotyrosine antibodies yielding complementary DNAs encoding active tyrosine kinases. The resulting clones were used to obtain the sequence of a novel 984 amino acid transmembrane tyrosine kinase. Analysis of the complementary DNA revealed extracellular immunoglobulin and fibronectin type III domains and the unusual kinase signature sequence KWIAIES; all are characteristic of the axl family of tyrosine kinases. The novel tyrosine kinase was not expressed in normal B- and T-lymphocytes but, unlike axl, was expressed in numerous neoplastic B- and T-cell lines. Transcripts for the novel receptor-like tyrosine kinase were detected in normal peripheral blood monocytes and bone marrow. One alternatively spliced transcript was detected which contained an insert in the membrane proximal region that could encode for a truncated, soluble receptor. Sequence comparison shows that the kinase may be the human protooncogene for the recently isolated chicken retroviral oncogene v-ryk (recently renamed v-eyk), a truncated tyrosine kinase whose expression by retroviral infection produced sarcomas in chickens. The intracellular domain of the human kinase shows 83% similarity and 71% identity to v-ryk. Since the ryk designation has been used to name another tyrosine kinase and an analysis of RNA expression demonstrated that this novel human kinase is expressed in monocytes and tissues of epithelial and reproductive origin, we have designated our novel protooncogene c-mer.

A cluster of patients with inferior rectus restriction following local anesthesia for cataract surgery

During a 5-month period, four patients developed contracture of the inferior rectus muscle following local anesthesia for cataract surgery in the practice of one ophthalmologist. Two anesthesiologists administered retrobulbar anesthesia. All patients had persistent vertical diplopia caused by a large hypotropia of the operated eye. Forced duction testing revealed marked restriction to elevation of the eye. In two patients, MRI demonstrated segmental thickening of the inferior rectus muscle, just posterior to the globe. All patients had normal thyroid function tests. No patient had a previous history of strabismus. Three of the four have had strabismus surgery consisting of recession of the markedly restricted inferior rectus muscle on an adjustable suture. These three patients have regained fusion and are now asymptomatic.

Mitochondria as a source of reactive oxygen species during reductive stress in rat hepatocytes

Cell killing, oxygen consumption, and hydroperoxide formation were determined in rat hepatocytes after glycolytic and respiratory inhibition. These conditions model the ATP depletion and reductive stress of anoxia ("chemical hypoxia"). Glycolysis was inhibited with iodoacetate, and mitochondrial electron transfer was blocked with sodium azide, cyanide, or myxothiazol. Cell killing, hydroperoxide formation, and inhibitor-insensitive oxygen consumption were greater after azide than after myxothiazol or cyanide. Desferrioxamine, an inhibitor of iron-catalyzed hydroxyl radical formation, delayed cell killing after each of the respiratory inhibitors. Anoxia also delayed cell killing during chemical hypoxia. However, during anoxic incubations, desferrioxamine did not delay the onset of cell death. These findings indicate that reactive oxygen species participate in lethal cell injury during chemical hypoxia. In isolated mitochondria, previous studies have shown that myxothiazol inhibits Q cycle-mediated ubisemiquinone formation in complex III (ubiquinol-cytochrome c oxidoreductase) and that ubisemiquinone can react with molecular oxygen to form superoxide. Decreased killing of hepatocytes with myxothiazol compared with azide suggests, therefore, that mitochondrial oxygen radical formation by complex III is involved in cell killing during reductive stress. In support of this hypothesis, myxothiazol reduced rates of cell killing and hydroperoxide formation in hepatocytes incubated with azide or cyanide. This mitochondrial mechanism for oxygen radical formation may be important in relative but not absolute hypoxia.

Homomeric GluR1 excitatory amino acid receptors expressed in Xenopus oocytes

The GluR1 cDNA clone encodes a functional excitatory amino acid receptor (Hollmann et al., Nature 342: 643-648 (1989]. We have studied the pharmacological properties of this homomeric (single subunit) receptor expressed in Xenopus oocytes and compared these properties with those of receptors encoded by rat forebrain mRNA. (RS)-alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionate, quisqualate, and glutamate were partial agonists at both GluR1 and forebrain non-N-methyl-D-aspartate (-NMDA) receptors. The potency of the agonists kainate, domoate, and glutamate was higher, and that of the antagonists 6-cyano-7-nitro-quinoxalinedione and 6,7-dichloro-3-hydroxy-2-quinoxaline carboxylic acid lower, for GluR1 receptors as compared with forebrain non-NMDA receptors. The GluR1 receptor differed strikingly from forebrain-derived non-NMDA receptors, however, in that it exhibited slow, calcium-dependent desensitization. Thus, most properties of the GluR1 receptor are similar but not identical to those of non-NMDA receptors expressed from forebrain mRNA. These results indicate that the ligand recognition sites on GluR1 homomeric receptors are subtly different from those of non-NMDA receptors expressed from a mixture of forebrain mRNA.

Protection by acidotic pH and fructose against lethal injury to rat hepatocytes from mitochondrial inhibitors, ionophores and oxidant chemicals

The importance of mitochondrial ATP formation and extracellular acidosis was evaluated in hepatocyte suspensions after different toxic treatments. Acidotic pH was protective against cell killing from all toxic treatments examined except for pronase, a toxic protease. Fructose, a substrate for glycolytic ATP formation, provided good protection against toxicity from cyanide, oligomycin, t-butyl hydroperoxide, menadione and cystamine. Protection by fructose against CCCP, gramicidin and Br-A23187 required oligomycin. This indicated that these ionophores were causing cytotoxicity by uncoupling oxidative phosphorylation. Fructose provided little protection against pronase and HgCl2, the latter compound being a potent inhibitor of glycolysis. In conclusion, disruption of mitochondrial ATP formation was a common event contributing to the toxicity of chemical oxidants and ionophores. Acidotic pH was generally protective under these conditions of impaired ATP generation.

A new method to monitor Kupffer-cell function continuously in the perfused rat liver. Dissociation of glycogenolysis from particle phagocytosis

In order to study particle phagocytosis and glycogenolysis simultaneously, this study was designed to develop a direct-read-out method to monitor Kupffer-cell function continuously, based on the uptake of colloidal carbon by the isolated perfused rat liver. Livers were perfused for 20 min with Krebs-Henseleit buffer saturated with O2/CO2 (19:1). Colloidal carbon (1-2 mg/ml) was added to the buffer, and absorbance of carbon was monitored continuously at 623 nm in the effluent perfusate. Since colloidal-carbon uptake was proportional to A623, rates of uptake were determined from the influent minus effluent concentration difference, the flow rate and the liver wet weight. Rates of colloidal-carbon uptake were 50-200 mg/h per g and were proportional to the concentration of carbon infused. Data from light-microscopy and cell-separation studies demonstrated that carbon was taken up exclusively by non-parenchymal cells and predominantly by Kupffer cells. Further, the amount of colloidal carbon detected histologically in non-parenchymal cells increased as the concentration of colloidal carbon in the perfusate was elevated. When Kupffer cells were activated or inhibited by treatment with endotoxin or methyl palmitate, carbon uptake was increased or decreased respectively. Taken together, these results indicate that Kupffer-cell function can be monitored continuously in a living organ. This new method was utilized to compare the time course of phagocytosis of carbon by Kupffer cells and carbohydrate output by parenchymal cells. Carbohydrate output increased rapidly by 69 +/- 9 mumol per g within 2-4 min after addition of carbon and returned to basal values within 12-16 min. However, carbon uptake by the liver did not reach maximal rates until about 15 min. Infusion of a cyclo-oxygenase inhibitor, aspirin (10 mM), caused a progressive decrease in carbohydrate output and blocked the stimulation by carbon completely. Aspirin neither altered rates of carbon uptake nor prevented stimulation of carbohydrate release by addition of N2-saturated buffer. The data from these experiments are consistent with the hypothesis that output of mediators by Kupffer cells, presumably prostaglandin D2 and E2, occurs transiently as Kupffer cells begin to phagocytose foreign particles in the intact organ, a process which continues at high rates for hours.

Toxic injury from mercuric chloride in rat hepatocytes

The relationship between cytosolic free Ca2+, mitochondrial membrane potential, ATP depletion, pyridine nucleotide fluorescence, cell surface blebbing, and cell death was evaluated in rat hepatocytes exposed to HgCl2. In cell suspensions, 50 microM HgCl2 oxidized pyridine nucleotides between 1/2 and 2 min, caused ATP depletion between 2 and 5 min, and produced an 89% loss of cell viability after 20 min. Rates of cell killing were identical in high (1.2 mM) and low (2.6 microM) Ca2+ buffers. Cytosolic free Ca2+ was determined in 1-day cultured hepatocytes by ratio imaging of Fura-2 employing multiparameter digitized video microscopy. In high Ca2+ medium, HgCl2 caused a 3-4-fold increase of free Ca2+ beginning after 6-7 min, but free Ca2+ did not change in low Ca2+ medium. Bleb formation occurred after about 4-5 min in both buffers prior to any increase of free Ca2+. Subsequently, in high Ca2+ medium, blebs became hot spots of free Ca2+ (greater than 600 nM). After about 2 min of exposure to HgCl2, rhodamine 123 fluorescence redistributed from mitochondrial to cytosolic compartments signifying collapse of the mitochondrial membrane potential. The results taken together demonstrate that bleb formation, ATP depletion, and the onset of cell death are not dependent on an increase of cytosolic free Ca2+. HgCl2 toxicity appears to be a consequence of inhibition of oxidative phosphorylation leading to ATP depletion and cell death.

Swelling, reductive stress, and cell death during chemical hypoxia in hepatocytes

In rat hepatocytes, we examined the relationship between cell volume, bleb formation, and loss of cell viability during chemical hypoxia with KCN plus iodoacetic acid. In hypotonic media (150-200 mosmol/kgH2O), cells swelled to a greater extent during chemical hypoxia than in isotonic media, but rates of cell killing were identical. Sucrose (300 mM) added to isotonic media prevented early cell swelling but actually accelerated cell killing. In contrast, mannitol (300 mM) improved cell survival but did not prevent cell swelling. Bleb formation occurred regardless of buffer tonicity. The antioxidants desferrioxamine and cyanidanol but not superoxide dismutase +/- catalase delayed lethal cell injury. Cell killing was greater during aerobic compared with anaerobic chemical hypoxia. Hydroperoxide formation was measured using a dichlorofluorescin assay and was accelerated during aerobic but not anaerobic chemical hypoxia. The results indicate that cell swelling is not the driving force for bleb formation or lethal cell injury. We conclude that "reductive stress" caused by respiratory inhibition favors formation of toxic oxygen species and may contribute to lethal cell injury during intermittent or incomplete oxygen deprivation.

Extracellular acidosis delays onset of cell death in ATP-depleted hepatocytes

A fluorometric assay using propidium iodide total fluorescence was utilized to quantitate cell viability in hepatocyte suspensions continuously. For viable hepatocytes exposed to KCN, fluorescence was linearly proportional to lactate dehydrogenase release and to nuclear labeling by propidium iodide. In KCN-treated hepatocytes, iodoacetate eliminated the protective effect of the fed state and fructose against the onset of cell death. A model of cell death with KCN and iodoacetate was developed to mimic the ATP depletion of anoxia. This "chemical hypoxia" was used to investigate the role of pH in cell death. At pH 7.4, cell viability decreased to 10% after 120 min, whereas at pH 5.5-7.0, cell viability was 65-85%, nearly the same as normoxic cells. During chemical hypoxia under acidotic conditions, a return of pH to 7.4 resulted in a rapid acceleration of cell killing, a "pH paradox." Inhibition of Na+-H+ exchange increased survival, whereas promoting exchange of intracellular Cl- for extracellular HCO3- potentiated cell killing. Monensin, a Na+-H+ ionophore, potentiated cell killing at pH 7.4 but not at pH 6.2. The results show that extracellular acidosis markedly protects against cell killing after ATP depletion, an effect that appears mediated through cytoplasmic acidification.