Chemical composition and anti-proliferative activity of essential oils from some medicinal plants from Cachicadán, Región La Libertad, Perú.

This study evaluated the chemical composition and anti-proliferative activity of essential oils (EOs) obtained by hydrodistillation from seven medicinal plants from Cachicadán, La Libertad Región, Perú. Limonene (0.64 to 44.43%) and linalool (0.36 to 2.12%) were identified in all EOs by gas chromatography coupled to mass spectrometry analysis. The major components (relative intensity ≥ 10%) were cis-dihydro carvone, carvone, and cis-piperitone epoxide for Minthostachys mollis leaves; ß-pinene, limonene, and ledol for Lepechinia heteromorpha leaves; limonene, neral, and geranial for Aloysia citriodora, both leaves and flowers; α-pinene, and limonene for Myrcianthes myrsinoides leaves; and α-pinene, ß-myrcene, and (E)-ß-Ocimene for Dalea carthagenensis leaves. Constituted by (Z)-ß-ocimene, dihydrotagetone, (Z)-tagetone, and car-3-en-2-one, EO of Tagetes minuta leaves induced an irreversible cytostatic effect against MCF-7 human breast tumor cells. Further in vivo studies must be carried out to establish the safe and efficient dose of T. minuta EO as adjuvant treatment in oncological therapies.

Seguridad alimentaria y fortificación de alimentos a base de pulpa de café en tiempos pandémicos

Introducción: la pandemia de COVID-19 originó pérdidas humanas, tensiones en la atención médica, la economía y otros sistemas sociales. Objetivo: recopilar información sobre seguridad alimentaria y fortificación de alimentos a base de pulpa de café considerando que una buena nutrición contrarresta las infecciones. Metodología: se analizó literatura en las bases SciELO y SCOPUS restringiendo términos de búsqueda a: seguridad alimentaria, COVID-19, tecnología de bloques o blockchain, suministro alimenticio, micronutrientes, regulación, fortificación con hierro con énfasis en productos a base de pulpa de café. Resultados: en tiempos de pandemia y otros desastres, uno de los factores que afectan la respuesta de un huésped al virus es la nutrición, la seguridad alimentaria es importante especialmente en países con altas tasas de desnutrición y anemia, por ende, es fundamental la fortificación de alimentos comunes para contribuir en garantizar la adecuación nutricional como parte de las respuestas de los gobiernos, especialmente en áreas rurales y urbanas empobrecidas, planteándose sistemas de suministro de alimentos con la tecnología de bloques o blockchain. Conclusión: la fortificación de productos alimenticios a base de pulpa de café y el suministro que aplique tecnología de bloques podría ser una estrategia de respuesta a las consecuencias de la pandemia

SUMMARY Introduction: The COVID-19 pandemic caused human losses, tensions in medical care, the economy and other social systems. Objective: To collect information on food safety and fortification of foods based on coffee pulp, considering that good nutrition counteracts infections. Methodology: Literature in SciELO and SCOPUS bases was analyzed, restricting search terms to food safety, COVID-19, block chain technology, food supply, micronutrients, regulation, iron fortification with emphasis on coffee pulp-based products. Results: In times of pandemic and other disasters, one of the factors that affect the response of a host to the virus is nutrition. The importance of food security is recognized with proposals especially in countries with high rates of malnutrition and anemia, for the fortification of common foods to contribute to guaranteeing nutritional adequacy as part of the governments' responses, especially in impoverished rural and urban areas, considering food supply systems with block or Block Chain technology. Conclusion: The fortification of food products based on coffee pulp and their supply using block chain could be a response strategy to the consequences of the pandemic.

Introdução: a pandemia de COVID-19 causou perdas humanas, tensões na assistência médica, na economia e em outros sistemas sociais. Objetivo: coletar informações sobre segurança alimentar e fortificação de alimentos à base de polpa de café, considerando que uma boa nutrição combate infecções. Metodologia: a literatura foi analisada nas bases de dados SciELO e SCOPUS, restringindo os termos de busca a: segurança alimentar, COVID-19, tecnologia de bloco ou blockchain, abastecimento de alimentos, micronutrientes, regulação, fortificação de ferro com ênfase em produtos à base de polpa de café. Resultados: em tempos de pandemia e outros desastres, um dos fatores que afeta a resposta de um hospedeiro ao vírus é a nutrição, a segurança alimentar é importante principalmente em países com altos índices de desnutrição e anemia, portanto, a fortificação é essencial dos alimentos comuns para ajudar a garantir a adequação nutricional como parte das respostas governamentais, especialmente em áreas rurais e urbanas empobrecidas, considerando sistemas de abastecimento de alimentos com tecnologia block ou blockchain. Conclusão: a fortificação de produtos alimentícios à base de polpa de café e abastecimento aplicando tecnologia de blocos pode ser uma estratégia de resposta às consequências da pandemia.

Transport of the Thyroid Hormone Carrier Protein Transthyretin into Human Epidermoid Cells.

Purpose: Transthyretin (TTR) is a protein with a growing number of biological functions in addition to its well-established binding and circulatory transport of thyroxine, and indirect retinoid transport through interaction with retinol-binding protein. Misfolded and aggregated wild-type and mutant TTRs are involved in amyloid diseases. Several aspects of TTR pathology and physiology remain poorly understood. Receptor-mediated cellular transport of TTR has been described in a few cell types; and such studies suggest the possibility of different TTR receptors and endocytic pathways. Our main objective was to further understand the endocytic pathways for TTR.Methods: In the current study, analyses of TTR endocytic transport were performed in the human A431 cell line. The results of TTR uptake were compared with those of the iron-carrier protein transferrin (Tf, a common stardard for endocytosis studies) in the same cell types.Results: A comparison of TTR and Tf endocytosis suggested similar early, 5-10 min, accumulation kinetics. But at a later time, 30 min, TTR accumulation was 20-30% lower than that of Tf (p < .05), a result that suggests different post-endocytic fates for these two ligands. Through the use of multiple endocytosis inhibitors, biochemical evidence is provided for an internalization pathway that differs from the clathrin-mediated endocytosis of Tf.Conclusions: These results for A431 cells are compared with others reported for different cell types; and it is suggested that this same hormone carrier protein can transit into cells through multiple endocytic pathways.

Endocytic Transport as a Drug Target in Infectious Diseases.

Components of the extracellular environment can be transported into cells by molecular mechanisms collectively termed endocytosis. Cells typically use a multitude of such internalization pathways. These endocytic transport pathways have a wide range of implications for physiological regulation as well as pathological processes. Many infectious diseases, for example, involve internalization of the pathogen into the cell as part of the infection process. Selective interference with the endocytic transport of a microbe, thus, represents a therapeutic strategy that may prevent infections or decrease the rate of their progression. Herein, we provide a brief review of strategies for discovery of novel anti-infection drugs and their pharmacological implications.

Cytotoxic Effects of Transthyretin Aggregates in an Epidermoid Cell Line.

OBJECTIVE: Skin amyloid deposits can occur as part of systemic amyloidoses including those involving misfolded- aggregated transthyretins (agTTR). Pathological effects of agTTR on the skin are not well understood. The main objective of the current study was to examine the toxicity of agTTR upon a human keratinocyte cell line. METHODS: Cells were analyzed for indicators of oxidative stress after treatment with normal soluble TTR or the same pre-aggregation concentration of agTTR. Hydrogen peroxide production was analyzed as an indicator for the involvement of reactive oxygen species. RESULTS: Treatment of cells with agTTR significantly increased hydrogen peroxide production (p < 0.05 vs. controls). Glutathione (GSH) and catalase were analyzed as indicators of endogenous cellular antioxidant activity. Treatment of cells with agTTR resulted in significant decreases in both catalase activity and GSH levels (p < 0.05 vs. controls). CONCLUSION: agTTR disrupts redox balance and induces oxidative stress in these epidermoid cells.

Disruption of endocytic transport by transthyretin aggregates.

The cytotoxicity of amyloidogenic proteins such as transthyretin (TTR) has implications for neurodegeneration and other pathologies, but is not well understood. In the current study, potential effects of misfolded, aggregated TTRs (agTTR) upon a major cell membrane function-endocytosis-were assessed. Internalization of transferrin (Tf), a ligand whose receptor-mediated endocytosis is well characterized, was analyzed in different cell types after treatment with agTTR. The results indicate disruption of Tf endocytosis: 20-25% inhibition by agTTR relative to the same concentrations of normal soluble TTR, or relative to another control protein, albumin (p<0.05 for agTTR relative to controls). No statistically significant difference was observed for cell surface Tf binding between agTTR-treated and control cells. This is the first evidence for endocytic disruption by agTTR, and presents a novel cytotoxicity mechanism that may account for previously reported inhibitory effects of amyloidogenic TTR on neuronal growth.

Activities of apocynin in cytotoxicity assays of potential pathological relevance.

Low levels of some reactive oxygen and nitrogen species (ROS, RNS) are of physiological importance; but high levels result in oxidative stress and can perturb many cell functions including signal transduction and transport, and contribute to aging and chronic diseases. Apocynin (1-(4-hydroxy-3-methoxyphenyl)ethanone) is a phytochemical with reported antioxidant activities in some experimental models of human disease. The major objectives of the current study were to test the antioxidant capacity of apocynin in a hemin-peroxide assay, and test its capacity to moderate pro-oxidant-dependent inhibition of a cell function-endocytic transport. Apocynin, tested at concentrations up to 20µM, did not exhibit statistically significant antioxidant activity (94.3±7.8% relative to controls, p>0.05) in the oxidation assay. When tested against the inhibition of endocytic transport by hydrogen peroxide, apocynin treatment did not significantly rescue such inhibition in the cell types tested (p>0.05, relative to peroxide alone). When cells were treated with a cytotoxic protein aggregate that increased both ROS and RNS, apocynin treatment only inhibited production of the latter (30.0±3.6% inhibition relative to controls without apocynin, p<0.05). The results provide evidence that apocynin, unlike other phytochemicals such as curcumin, does not exhibit antioxidant activity in the heme-peroxide assay. The results also provide the first evidence that apocynin does not rescue hydrogen peroxide-mediated inhibition of endocytic transport, nor prevent hydrogen peroxide production by a cytotoxic protein aggregate. In the latter toxicity assay, however, apocynin could moderate oxidative stress by decreasing cellular levels of RNS.

Pro-oxidative effects of aggregated transthyretin in human Schwannoma cells.

Neurotoxicity mechanisms of amyloidogenic polypeptides such as transthyretin (TTR) are not well understood. Misfolded and aggregated TTRs (agTTR) lead to age-related diseases such as senile systemic amyloidosis and familial amyloid polyneuropathy (FAP). Among other clinical manifestations in TTR amyloidic disease, peripheral nerve tissue, including Schwann cell, degeneration has been observed. In this study, we examined potential toxic effects of agTTR in human Schwannoma cells (sNF94.3 peripheral nerve sheath line). Cells were treated with agTTR (2.4µM pre-aggregation concentration) or, as controls, normal, soluble TTR (2.4µM) or no-TTR treatment, and then analyzed for different pro-oxidant and anti-oxidant markers: hydrogen peroxide (H2O2), catalase (CAT), glutathione (GSH), and more generalized cellular antioxidant capacity. In the latter case, cytosolic fractions were prepared after agTTR (or control) treatments and analyzed in oxidation assays. Relative to treatment with normal soluble TTR, cells treated with agTTR increase their release of H2O2. Residual CAT activity is decreased after agTTR treatment. The Schwannoma cells also exhibit significantly lower levels of GSH after agTTR treatment (p<0.05, relative to controls). More generally, cytosols from agTTR-treated cells exhibited a lower capacity to prevent oxidation relative to those from control cells (TTR-treated, or non-TTR-treated). These results suggest that agTTR (a) stimulates production of reactive oxygen species, (b) leads to lower levels of endogenous antioxidants, and (c) decreases overall cellular antioxidant capacity, in Schwannoma cells.

Transthyretin aggregates induce production of reactive nitrogen species.

BACKGROUND AND OBJECTIVE: Misfolded and aggregated transthyretins (agTTR) contribute to neurodegenerative amyloid diseases such as familial amyloid polyneuropathy and senile systemic amyloidosis. The neurotoxicity mechanisms of agTTR, however, are not well understood. In the current study, the possible contribution of reactive nitrogen species (RNS) to such mechanisms was investigated by examining agTTR-mediated changes in cellular RNS levels. METHODS AND RESULTS: The production of RNS was assessed through nitrate and nitrite assays in two human cell lines after exposure to agTTR (2.4 µM pre-aggregation concentration). In both epidermoid (A431) and schwannoma (sNF94.3) cell lines, agTTR induced significant increases in RNS (p < 0.05 relative to the same concentration of normal TTR, or no-TTR controls). Redox modulators such as apocynin (1-(4-hydroxy-3-methoxy-phenyl)ethanone) and L-NMMA (N(G)-monomethyl-L-arginine) were tested for their effects on RNS production. These modulators decreased RNS production in both cell lines; although the effects of L-NMMA were statistically significant only in the schwannoma cells. Moreover, cells treated with agTTR exhibited decreases in metabolic activity relative to TTR- or non-TTR-treated cells (p < 0.05) as assessed by reduction of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). CONCLUSION: The results provide novel evidence for involvement of RNS in pro-oxidative effects of agTTR in two different human cell lines, and show that agTTR can induce more generalized changes in cellular metabolic activity.

Ligand-peroxidase conjugates for quantification of receptor-mediated transport into cells.

Receptor-mediated cellular uptake of physiological regulators such as nutritional and hormonal factors represents a transport event with important consequences for cell differentiation, death, or proliferation. Although internalization pathways are important points of regulation, they have not been extensively explored as pharmacological targets in most cell types. An experimental strategy based on ligand-enzyme conjugates is presented in this report that may facilitate high-throughput screening for potent chemical modulators of the transport events. The method was tested on a human epidermoid cell line using a streptavidin-peroxidase conjugate, and human holo-transferrin as the model ligand, in a biotin-ligand conjugate. The proposed screening method is rapid, can be performed using multi-well plates, and involves small assay volumes. The modular nature of the ligand complex makes this method adaptable to the use of other biotinylated ligands, and the use of avidins conjugated to other enzymes. As is discussed, the method may also be applicable to other in vitro and in vivo transport assays.

An assessment of dietary flavonoid intake in the UK and Ireland.

Accurate estimates of flavonoid intake are important for public health studies and potential policies related to these phytochemicals. As an alternative to studies involving population samples and individual food consumption surveys, the international FAO Food Balance Sheets (FBS) were used in the current study to estimate flavonoid consumption among the populations of the UK and Republic of Ireland. A supplemented USDA database was prepared for flavonoid analyses of the foods reported in the FBS. Twenty-three flavonoids from five groups (anthocyanidins, flavonols, flavanols, flavanones, and flavones) were analyzed. Estimated per-capita daily flavonoid intake (all five groups) was 182 mg and 177 mg for the UK and Ireland, respectively. In both cases, anthocyanidins and flavanols accounted for about 65% of total consumption. Combined intake of flavones, flavanones, and flavonols was 60 mg/day in the UK and 69 mg/day in Ireland. These flavonoid intake values are compared with those previously reported for the UK and other countries. Overall, these novel results contribute to establishing accurate reference points for national flavonoid intakes.

Comparative antioxidant activities and synergism of resveratrol and oxyresveratrol.

Resveratrol (1) and oxyresveratrol (2) are phytoalexins with antioxidant activities (AAs) and proposed effects against several pathological processes. The main objective of this study was to provide a novel, comparative assessment of their AAs, and to test for potential synergism in their combined activities, or in combination with another phytochemical antioxidant, curcumin (3). The phytochemicals were tested at 10 µM total concentrations in a heme-based assay that involved, as the final step, quantification of tetramethyl-phenylene-diamine oxidation. Significant AAs were observed for both 1 and 2, 27-33% inhibition of oxidation (p < 0.05 relative to non-phytochemical control). The combination of 1 and 2 in the same assay (5 µM each) suggested a moderate synergistic effect of about 10% (41% inhibition of oxidation by 1/2 under the same conditions as for 1 and 2 separately). Combinations of 1/3 and 2/3 were also synergistic, but 1/3 had a two-fold greater AA (p < 0.05) than 2/3 (or 1/2). Our results indicate that (i) 1 and 2 are effective antioxidants in the assay, (ii) in combination, their AAs can synergise, and (iii) in relation to 2, 1 has a much greater synergistic potential with 3. The latter suggests different synergy mechanisms of the curcuminoid with each of the two stilbene phytoalexins.

Flavonoid intake and disability-adjusted life years due to Alzheimer's and related dementias: a population-based study involving twenty-three developed countries.

OBJECTIVE: Dietary flavonoids and their metabolites may have neuroprotective effects against age-associated neurodegenerative disorders such as Alzheimer's and related dementias (dementia). There is a lack of population studies, however, on correlations between flavonoid intake and dementia. The main objective of the present study was to analyse such a relationship at a large-scale population level. DESIGN: Based on global data (FAO, WHO), databases were generated for: (i) flavonoid content of foods; (ii) per capita national dietary intakes of flavonoids and other dietary factors; and (iii) disability-adjusted life years - a measure of burden and death - due to dementia. Five major flavonoid subclasses were examined. To minimize influences due to accuracy and reliability of the disease source data, twenty-three developed countries were selected after statistical evaluation. RESULTS: Flavonols and combined flavonoids (all five combined) intakes were the only two parameters with significant (P < 0.05) negative dementia correlations. Multiple linear regression models confirmed this relationship, and excluded confounding from some other dietary and non-dietary factors. Similar analyses with non-dementia, neurological/psychiatric diseases did not yield significant correlations. CONCLUSIONS: At a global level, and in the context of different genetic backgrounds, our results suggest that higher consumption of dietary flavonoids, especially flavonols, is associated with lower population rates of dementia in these countries.

A meta-analysis of medicinal plants to assess the evidence for toxicity.

Toxicity of phytochemicals, plant-based extracts and dietary supplements, and medicinal plants in general, is of medical importance and must be considered in phytotherapy and other plant uses. We show in this report how general database analyses can provide a quantitative assessment of research and evidence related to toxicity of medicinal plants or specific phytochemicals. As examples, several medicinal plants are analyzed for their relation to nephrotoxicity and hepatotoxicity. The results of analyses in different databases are similar, and reveal the two best-established toxic effects among the group of plants that were examined: nephrotoxicity of Aristolochia fangchi and hepatotoxicity of Larrea tridentata.

Protective activities of Vaccinium antioxidants with potential relevance to mitochondrial dysfunction and neurotoxicity.

Both the neurotransmitter dopamine (DA) and a neurotoxic metabolite, 6-hydroxy DA, can be oxidized to generate hydrogen peroxide and other reactive species (ROS). ROS promote oxidative stress and have been implicated in dopaminergic neurodegeneration, e.g., Parkinson's disease (PD). There is also evidence for a relation between catecholamine-mediated oxidative damage in dopaminergic neurons and the effects of these neurotransmitters on the redox state of cytochrome c (Cytc). In neurons and other cells, oxidative stress may be enhanced by abnormal release of Cytc and other mitochondrial proteins into the cytoplasm. Cytc release can result in apoptosis; but sub-apoptogenic-threshold release can also occur, and may be highly damaging in the presence of DA metabolites. Loss of mitochondrial membrane integrity, a pathological situation of relevance to several aging-related neurodegenerative disorders including PD, contributes to release of Cytc; and the level of such release is known to be indicative of the extent of mitochondrial dysfunction. In this context, we have used a Cytc-enhanced 6-hydroxy DA oxidation reaction to gauge dietary antioxidant activities. Anthocyanin-rich preparations of Vaccinium species (Vaccinium myrtillus, Vaccinium corymbosum, and Vaccinium oxycoccus) as well as a purified glycosylated anthocyanidin were compared. The most potent inhibition of oxidation was observed with V. myrtillus preparation: 50% inhibition with 7 microM of total anthocyanins. This activity was 1.5-4 times higher than that for the other preparations or for the purified anthocyanin. Ascorbate (Vitamin C), at up to 4-fold higher concentrations, did not result in significant inhibition in this assay. Antioxidant activity in the assay correlated strongly (r2>0.91, P<0.01) with reported Vaccinium content of anthocyanins and total cyanidins, but not quercetin or myricetin. The results provide evidence for the high potency of anthocyanins towards a potentially neurotoxic reaction, and provide a basis for in vivo testing of these flavonoids and their physiological metabolites in the context of neuro- and mitochondrio-protective effects.

DNA methylation, riboswitches, and transcription factor activity: fundamental mechanisms of gene-nutrient interactions involving vitamins.

Nutrient-gene interactions occur with a variety of nutrients including some minerals, vitamins, polyunsaturated fatty acids and other lipids. Fundamental molecular mechanisms that underlie many of the effects of nutrients on gene expression are presented herein. Two of the mechanisms described influence gene transcription: DNA methylation and transcription factor activation. Another mechanism, riboswitching, can regulate gene expression at different levels, for example, at the mRNA translation level. The first two mechanisms are widely distributed across animal phyla. Riboswitches are documented primarily in more primitive organisms, but may prove to be of wider relevance. Riboswitches are known for several vitamins; those involving thiamine are presented here. The role of folates and retinoids in DNA methylation and transcriptional factor (nuclear retinoid receptor) activities, respectively, is presented in the context of cell proliferation and differentiation, and related physiological or pathological effects during embryogenesis and cancer.

Oxidative stress disrupts internalization and endocytic trafficking of transferrin in a human malignant keratinocyte line.

Oxidative stress is involved in epidermal cell pathology. One potential mechanism for this toxicity that has previously not been explored in epidermal cells involves modulation of endocytic trafficking and the implications that such modulation can have for altered cell function. The effects of oxidative stress on endocytic trafficking are not well understood, particularly relating to how general or cell-type specific such effects may be. With induction of oxidative stress by hydrogen peroxide, for example, both impaired and enhanced cell-surface binding and endocytic trafficking have been reported for transferrin (Tf), a circulatory iron-carrier protein. The objective of the current study was to characterize the effect of oxidative stress on internalization and endocytic trafficking of Tf in an epidermoid cell line (A431). Evidence is presented for a significant dose-dependent impairment of cellular Tf internalization after treatment with hydrogen peroxide over a wide range of concentrations from 0.06 to 5.8 mM. Scatchard analysis of binding revealed that peroxide treatments resulted in a large decrease, more than fourfold, in the number of cell-surface Tf-binding sites (Bmax) but little change in the dissociation constant (Kd). With respect to endocytic trafficking of Tf, evidence is presented that transport of internalized transferrin back out of the cell (i.e., Tf recycling) is significantly impaired as a result of oxidative stress at all the peroxide concentrations tested. The oxidative stress-dependent changes in endocytic trafficking in these malignant human keratinocytes are compared with those reported for other cell types.

Comparative genetic mutation frequencies based on amino acid composition differences.

Genetic variation inferred from large-scale amino acid composition comparisons among genomes and chromosomes of several species, Saccharomyces cerevisiae, Drosophila melanogaster, Ceanorhabditis elegans, H. sapiens, is shown to be correlated (highest, r(2)=0.9855, p<0.01) with reported mutation rates for various genes in these species. This study, based largely on pseudogene data, helps to establish reference mutation frequencies that are likely to be representative of overall genome mutation rates in each of the species examined, and provides further insight into heterogeneity of mutation rates among genomes.

Evidence for a specific cell membrane retinol-binding protein transport mechanism in a human keratinocyte line.

The epidermis is highly sensitive to retinoids, and vitamin A (retinol) is a critical factor in the regulation of skin cell differentiation and proliferation. Despite extensive knowledge of retinoid-mediated gene transcription effects on epidermal cells and evidence for retinoid-mediated suppression of carcinogenesis in skin, basic transport events, especially cellular uptake, of this vitamin remain poorly understood and controversial. Herein, evidence is presented for receptor-mediated uptake of retinol-binding protein, RBP, the specific circulatory vitamin A carrier, in the A431 human epidermal cell line. Cellular RBP uptake was significantly inhibited by anti-RBP IgG. Addition of transthyretin (TTR), a circulatory protein that can interact with RBP, to the internalization assay also significantly reduced RBP uptake to 49.4+/-4.6% (+/- SEM) of control values (p<0.01). RBP uptake was impaired by sucrose, a known inhibitor of early endocytosis, but not significantly affected by a disruptor of later trafficking events, chlorpromazine. Binding analysis indicated saturable RBP binding to the cell surface and a total of about 94,000 binding sites/cell. Based on dissociation constants, two RBP binding sites were detected with a 50-fold affinity difference: 0.7 and 35.0 nM, with 12,000 and 82,000 receptors/cell, respectively. These results indicate that high affinity RBP receptors capable of internalizing RBP independently of TTR exist in these malignant keratinocytes, and that TTR influences binding of RBP to its putative receptor(s). Overall, the data establish membrane transport parameters for RBP, and provide a basis for examining modulation of vitamin A endocytosis that may accompany changes in proliferation or differentiation state of epidermal cells.

Modeling robust oscillatory behavior of the hypothalamic-pituitary-adrenal axis.

A mathematical model of the hypothalamic-pituitary-adrenal (HPA) axis of the human endocrine system is proposed. This new model provides an improvement over previous models by introducing two nonlinear factors with physiological relevance: 1) a limit to gland size; 2) rejection of negative hormone concentrations. The result is that the new model is by far the most robust; e.g., it can tolerate at least -50% and +100% perturbations to any of its parameters. This high degree of robustness allows one, for the first time, to model features of the system such as circadian rhythm and response to hormone injections. In addition, relative to its closest predecessor, the model is simpler; it contains only about half of the parameters, and yet achieves more functions. The new model provides opportunities for teaching endocrinology within a biological or medical school context; it may also have applications in modeling and studying HPA axis disorders, for example, related to gland size dynamics, abnormal hormone levels, or stress influences.