M. A . Visconti | Universidade de São Paulo (original) (raw)

Papers by M. A . Visconti

The adverse effects of tris (hydroxymethyl)-aminomethane (Tris) are for the first time reported o... more The adverse effects of tris (hydroxymethyl)-aminomethane (Tris) are for the first time reported on melanophore responses to agonists and potassium chloride. 2. Melanophore responses in Tris-or bicarbonate-buffered solutions were compared. 3. In the presence of Tris, the cumulative dose-response curve to norepinephrine was significantly shifted to the left. whereas methoxamine dose-response curves were similar in both buffers. 4. The percentage aggregation in response to synthetic MCH (melanin concentrating hormone) was not affected by Tris in the bathing medium. 5. The cumulative dose-response curve to potassium chloride was leftward shifted (one log case) in Tris-buffered solution. 6. These results suggest that in fish melanophore preparations Tris might exert its actions on the presynaptic membrane and/or on the synaptic cleft enzyme COMT, drawing on a greater availability of neurotransmitters at the melanophore membrane receptors.

analogue to vulgar vitiligo dermo-epidermal minigrafts 1Hospital Municipal Dr. Fernando Mauro Pir... more analogue to vulgar vitiligo dermo-epidermal minigrafts 1Hospital Municipal Dr. Fernando Mauro Pires da Rocha and

Brazilian Journal of Medical and Biological Research, 2012

Vertebrates have a central clock and also several peripheral clocks. Light responses might result... more Vertebrates have a central clock and also several peripheral clocks. Light responses might result from the integration of light signals by these clocks. The dermal melanophores of Xenopus laevis have a photoreceptor molecule denominated melanopsin (OPN4x). The mechanisms of the circadian clock involve positive and negative feedback. We hypothesize that these dermal melanophores also present peripheral clock characteristics. Using quantitative PCR, we analyzed the pattern of temporal expression of Opn4x and the clock genes Per1, Per2, Bmal1, and Clock in these cells subjected to a 14-h light:10-h dark (14L:10D) regime or constant darkness (DD). Also, in view of the physiological role of melatonin in the dermal melanophores of X. laevis, we determined whether melatonin modulates the expression of these clock genes. These genes show a time-dependent expression pattern when these cells are exposed to 14L:10D, which differs from the pattern observed under DD. Cells kept in DD for 5 days exhibited overall increased mRNA expression for Opn4x and Clock, and a lower expression for Per1, Per2, and Bmal1. When the cells were kept in DD for 5 days and treated with melatonin for 1 h, 24 h before extraction, the mRNA levels tended to decrease for Opn4x and Clock, did not change for Bmal1, and increased for Per1 and Per2 at different Zeitgeber times (ZT). Although these data are limited to one-day data collection, and therefore preliminary, we suggest that the dermal melanophores of X. laevis might have some characteristics of a peripheral clock, and that melatonin modulates, to a certain extent, melanopsin and clock gene expression.

Journal of Experimental Zoology, 1999

Skins of Potamotrygon reticulatus are light in color in vitro, exhibiting punctate melanophores. ... more Skins of Potamotrygon reticulatus are light in color in vitro, exhibiting punctate melanophores. Alpha-Melanocyte stimulating hormone (EC(50) = 4.58 x 10(-9) M) and prolactin (EC(50) = 1.44 x 10(-9) M) darken the skins in a dose-dependent manner. The endothelins ET-1, ET-2 and ET-3, and the purines, ATP, and uracil triphosphate (UTP) were not able to induce either skin lightening or darkening. Forskolin and the calcium ionophore A23187 promoted a dose-dependent darkening response, whereas N(2), 2'-O-dibutyryl guanosine 3'-5'-cyclic monophosphate (db cyclic GMP), phorbol-12-myristate-13-acetate (TPA), and 1-oleoyl-2-acetyl-sn-glycerol (OAG) were ineffective. The maximal response obtained with the calcium ionophore A23187 was only 76% of maximal darkening. These results indicate that the cyclic adenosine 3'-5'-monophosphate (cAMP) pathway is probably involved in the pigment dispersion of P. reticulatus melanophores. Other experiments should be done to further investigate how cytosolic calcium may be physiologically increased, and the existence of a putative cross-talk between calcium and cAMP signals. In conclusion, the only hormones effective on P. reticulatus melanophores were prolactin and alpha-MSH. No aggregating agent has been shown to antagonize these actions. Prolactin effect on elasmobranch melanophores adds a novel physiological role to this ancient hormone. J. Exp. Zool. 284:485-491, 1999.

Pigment Cell Research, 1989

Melanin concentrating hormone (MCH) is a cyclic heptadecapeptide, Asp-Thr-Met-Arg-Cys-Met-Val-Gly... more Melanin concentrating hormone (MCH) is a cyclic heptadecapeptide, Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val, synthesized in the hypothalamus and released by the neurohypophysis of teleost fish. This hormone is a potent lightening agent of fish skin. This lightening results from the stimulation of a centripetal melanosome (melanin granule) migration to a perinuclear position within integumental melanophores. MCH and related fragment analogues, MCHSi7 and MCH,-,, were used to investigate the ionic requirements for receptor activation by MCH on dermal melanophores of the fish Poecilia reticulntn. In calcium-free saline, the sensitivity of the melanophores to MCH and MCHi-14 increased, whereas the sensitivity of the cells to MCHS17 decreased. Verapamil diminished the sensitivity to MCHj17, but did not affect melanophore responses to MCH or MCHI-,,. The melanosome aggregating response to MCH was not affected in the presence of tetrodotoxin or in sodiumor potassium-free (choline-substituted) saline. These results suggest that neither TTX-sensitive sodium channels nor extracellular sodium or potassium ions play a role in MCH-induced melanosome aggregation. It is known that MCH and MCHl-L4 also exhibit MSH-like melanosome dispersion within melanophores, skin darkening activity on fish melanophores whereas MCHjl7 lacks this characteristic. Since the darkening activity of MCH and MCHI-11 requires calcium, these analogues exhibited a diminished lightening (MCHlike) activity in the presence of the divalent cation. In the absence of the Nterminal tetrapeptide sequence (necessary for the expression of MSH-like activity), a role for calcium on melanosome aggregation became evident. These results demonstrate a bifunctional role of calcium on melanosome movements.

Comparative Biochemistry and Physiology Part B: Comparative Biochemistry, 1992

1. Salmon melanin concentrating hormone (MCH) is a cyclic heptadecapeptide possessing the followi... more 1. Salmon melanin concentrating hormone (MCH) is a cyclic heptadecapeptide possessing the following primary structure: Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val. 2. In the fish, Synbranchus marmoratus, skin bioassay MCH5-15 is equipotent to MCH whereas MCH5-14, which comprises only the ring structure, is about 100-fold less active. 3. MCH and two fragment analogues, MCH5-15 and MCH5-14, were studied to determine their relative stability in the presence of fish serum and purified proteolytic enzymes, trypsin and alpha-chymotrypsin. 4. After 4 hr incubation in fish serum, MCH5-15 retained 1/100, MCH5-14 1/1000 and MCH only 6/1000 of the potency of the native hormone. 5. The three peptides were also very resistant to degradation by purified proteolytic enzymes involving the following relative order of resistance: MCH5-14 > MCH5-15 > MCH. MCH5-14 potency was not altered after a 1 hr incubation in either enzyme whereas MCH retained 1/10 and 4/100 of its original potency, and MCH5-15 retained 1/10 and 8/10 of its original potency, after 1 hr in trypsin and alpha-chymotrypsin, respectively.

Anais da Academia Brasileira de Ciências, 1985

We report here the effects of cytochalasin B, colchicine and vinblastine on melanosome migration ... more We report here the effects of cytochalasin B, colchicine and vinblastine on melanosome migration in Papiliochromis ramirezi melanophores. Melanosome migration was not affected by 2 X 10(-5) M cytochalasin B. On the other hand, the aggregation, usually elicited by 10(-6) M norepinephrine, was completely inhibited by simultaneous treatment with 10(-3) M colchicine and cold (0-3 degrees C). Same results were obtained with 10(-3) M vinblastine. Lower concentrations of colchicine had no effect on granule aggregation. However, the aggregation in 50% of the melanophores was still blocked by 10(-5) M vinblastine, whereas 10(-7) M vinblastine was ineffective. Melanosome dispersion usually elicited by 10(-3) M theophylline was significantly accelerated by 10(-3) M colchicine, but delayed by 10(-3) M vinblastine. Lower concentrations of both agents had no effect on pigment dispersion. Therefore our results strongly suggest that microtubule structural integrity is essential to P. ramirezi melan...

Progress in clinical and biological research, 1988

Comparative Biochemistry and Physiology Part C: Comparative Pharmacology, 1991

Beneficial cutaneous bacteria on amphibians can protect against the lethal disease chytridiomycos... more Beneficial cutaneous bacteria on amphibians can protect against the lethal disease chytridiomycosis, which has devastated many amphibian species and is caused by the fungus Batrachochytrium dendrobatidis. We describe the diversity of bacteria on red-backed salamanders (Plethodon cinereus) in the wild and the stability of these communities through time in captivity using cultureindependent Illumina 16S rRNA gene sequencing. After field sampling, salamanders were housed with soil from the field or sterile media. The captive conditions led to different trajectories of bacterial communities. Eight OTUs present on 490% of salamanders in the field, through time, and in both treatments were defined as the core community, suggesting that some bacteria are closely associated with the host and are independent of an environmental reservoir. One of these taxa, a Pseudomonas sp., was previously cultured from amphibians and found to be antifungal. As all host-associated bacteria were found in the soil reservoir, environmental microbes strongly influence host-microbial diversity and likely regulate the core community. Using PICRUSt, an exploratory bioinformatics tool to predict gene functions, we found that core skin bacteria provided similar gene functions to the entire community. We suggest that future experiments focus on testing whether core bacteria on salamander skin contribute to the observed resistance to chytridiomycosis in this species even under hygenic captive conditions. For disease-susceptible hosts, providing an environmental reservoir with defensive bacteria in captive-rearing programs may improve outcomes by increasing bacterial diversity on threatened amphibians or increasing the likelihood that defensive bacteria are available for colonization.

Journal of Experimental Zoology, 1999

Total serum IgM levels were studied in 84 mothers of infants with group-B streptococcal (GBS) sep... more Total serum IgM levels were studied in 84 mothers of infants with group-B streptococcal (GBS) septicemia/meningitis and compared to IgM concentrations in 91 parturients who were urogenital carriers of GBS but nevertheless gave birth to healthy infants. In all, 22 (27%) in the study group showed IgM levels above the arbitrarily selected limit of 2.40 g/1, in contrast to 12 (13%) of 91 controls (p = 0.02). Among the study group members whose infants were infected with GBS type III, 8 of 34 (24%) were high in serum IgM, com pared to only 2 of 34 (6%) of the corresponding controls (p = 0.04). The total serum IgG levels did not differ be tween the two groups.

Comparative Biochemistry and Physiology Part C: Comparative Pharmacology, 1984

Pigment Cell Research, 1990

An in vitro crustacean (freshwater shrimp, Macrobrachiurn potiuna) erythrophore bioassay for chro... more An in vitro crustacean (freshwater shrimp, Macrobrachiurn potiuna) erythrophore bioassay for chromatophorotropins and other pigment cell agonists is described. The present assay is a quantitative method that determines the pigment responses with the aid of an ocular micrometer. The pigment granules within the erythrophores are dispersed out into the dendritic processes of the cells when the isolated carapace is placed in physiological solution. This bioassay provides, therefore, a method for measuring the response of the pigment cells to aggregating agents such as pigment concentrating hormone (PCH). This bioassay is sensitive to PCH at a concentration as low as 3 x 10-12M. Calcium ionophore A23187 mimics the actions of PCH, but, unlike the hormone, the ionophoreinduced pigment aggregation is irreversible after physiological solution rinses. Therefore, chromatophorotropic activities of pigment dispersing agents, such as pigment dispersing hormones (PDH), can be determined on ionophore-treated erythrophores. The potencies of a-PDH and p-PDH show a threefold difference (not significant). Because of its convenience and its ability to make an objective determination of the bidirectional pigment movements within erythrophores, this bioassay is a suitable method for further structure-activity studies of the various chromatophorotropins and their analogs.

Pigment Cell Research, 1990

Norepinephrine (NE) and phenylephrine (Phe) were employed to study the ionic requirements for alp... more Norepinephrine (NE) and phenylephrine (Phe) were employed to study the ionic requirements for alpha adrenoceptor activation in the teleost Poeciliu reticulutu melanophores. As expected the beta adrenoceptor blocker, propranolol, increased the sensitivity of the preparation to NE (5.8 times), and was therefore employed in all the experimental procedures. Neither cocaine (a neuronal uptake blocker) nor dexamethasone (an extraneuronal uptake blocker) enhanced the sensitivity of the preparation to NE, suggesting that these inactivating mechanisms would not play a role in P. reticulutu pigmentary system. However, in the absence of calcium, the dose-response curve (DRC) to NE was displaced to the left about 3.5 times, whereas the DRC to Phe was not affected. These results indicate that a neuronal uptake is active, but was not demonstrated by the classical pharmacological tools, probably due to an assymmetric display of the nervous endings. The DRC to NE was rightward displaced (14.1 times) in the presence of the calcium channel blocker Verapamil, whereas the DRC to Phe was not affected. These data suggest that P. reticulutu melanophores possess a mixed population of alphal and alphaz adrenoceptors, the activation of the latter eliciting an extracellular calcium influx. In sodium-free saline, the DRC to NE was rightward shifted (6.6 times) and the response to Phe was impaired in such a way that the maximal response was not achieved. The DRC to both NE and Phe were rightward displaced (7.9 and 2.7 times respectively) in the presence of the sodium channel blocker tetrodotoxin (TTX) 10-'M. In potassium-free saline, the melanophore sensitivity to Phe was increased, whereas the responses to NE were not affected, suggesting a differential sensitivity of the two alpha adrenoceptor subtypes to the resulting membrane hyperpolarization. Based on the literature and on our data we propose that P. reticulutu melanophores possess a mixed population of alphal and alphaz receptors. The activation of both subtypes of alpha adrenoceptors elicits a Na+ ion influx through TTX-sensitive sodium channels. The stimulation of alpha, adrenoceptors also requires an extracellular calcium influx, through the opening of slow calcium channels.

Mini-Reviews in Medicinal Chemistry, 2005

Medicinal Chemistry, 2008

In vivo and in vitro assays were performed with S91 murine melanoma cells aiming to investigate t... more In vivo and in vitro assays were performed with S91 murine melanoma cells aiming to investigate the effects of testosterone and photoperiod on tumor growth and melanogenesis (tyrosinase activity). In vivo assays were performed by inducing melanoma tumors in castrated mice receiving increasing concentrations of testosterone and submitted to varying photoperiod regimens. The results demonstrated that the increase of melanin content was higher in animals submitted to the longest days, thus demonstrating the importance of photoperiod length in melanin synthesis. Increase in tumor growth and protein content was observed in testosterone-treated animals submitted to 12L:12D; in testosterone-treated animals submitted to 4L:20D and 20L:4D tumor growth was significantly smaller. In S91 cultured cells, testosterone increased cell proliferation and reduced tyrosinase activity in a dose-dependent manner. Radioactive binding assays demonstrated that the hormone was acting through low affinity testosterone receptors, since the presence of aromatase inhibitor did not affect the binding assay in a statistically significant way, and all the in vitro experiments were performed in the presence of the inhibitor. Our in vivo data added to the in vitro results corroborate the hypothesis that S91 melanoma cells directly respond to testosterone and that this effect is modulated by light.

Life Sciences, 1987

H-Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val-OH , melanin concentrating ... more H-Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val-OH , melanin concentrating hormone (MCH), exhibits both melanin granule concentrating and dispersing (MSH-like) activities. Fragment analogues of MCH were synthesized as described herein and the melanotropic activities of the peptides were determined. In the frog (Rana pipiens) and lizard (Anolis carolinensis) skin bioassays, the 5-17 and 5-14 fragments of MCH were inactive (at concentrations of 10(-5)M or less), whereas the 1-14 sequence exhibited minimal (about 10%) MSH-like activity compared to MCH, which, as reported previously, was about 600 times less active than alpha-MSH. In the teleost (fish) skin bioassay, the MCH5-17 analogue was equipotent to MCH, whereas the 1-14 analogue was 10-30 times and the cyclic N- and C- terminal truncated analogue, MCH5-14, was about 300 times less active than MCH. These results suggest that the N-terminal sequence is particularly critical to MSH-like activity in the tetrapod species studied, whereas other structural regions of MCH, particularly in the C-terminal, are more related to MCH activity in teleosts.

General and Comparative Endocrinology, 2008

Insulin is the hormone that plays an essential role in metabolism and mitosis of normal and tumor... more Insulin is the hormone that plays an essential role in metabolism and mitosis of normal and tumor cells, exerting its pleiotropic effects through binding to specific membrane receptors and promoting the phosphorylation of tyrosine residues of the receptor itself and of other components of the signaling pathway. The aim of this study was to investigate the effects of insulin on melanogenesis and cell growth in three different cell lines: the goldfish GEM-81 erythrophoroma cells (undifferentiated and differentiated with 1.5% dimethylsulfoxide-DMSO), and the murine B16F10 and Cloudman S91 melanoma cells. Undifferentiated GEM-81 and B16F10 cells responded to insulin with a small increase of cell proliferation, whereas S91 cells responded with a decrease of growth. In the two mammalian cell lines, and in DMSO-differentiated GEM-81 cells, the hormone strongly inhibited melanogenesis, by decreasing tyrosinase activity. In undifferentiated GEM-81 cells, insulin had no effect on tyrosinase activity. An increase in the tyrosine phosphorylation status of pp185 (insulin receptor substrate 1 and 2-IRS-1/2) phosphorylation degree was observed in S91 mouse melanoma and in differentiated GEM-81 erythrophoroma cells, suggesting that this specific protein was maintained during transformation process and participates in insulin signaling. Our results imply an ancient and diverse history of the insulin signaling system in vertebrate pigment cells.

FEBS Letters, 2001

Similar to melanocyte stimulating hormone (K K-MSH), its potent and long-acting analogue, [Nle 4 ... more Similar to melanocyte stimulating hormone (K K-MSH), its potent and long-acting analogue, [Nle 4 , D-Phe 7 ]K K-MSH, when labeled with the paramagnetic amino acid probe 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid (Toac), maintains its full biological potency, thus validating any comparative structural investigations between the two labeled peptides. Correlation times, calculated from the electron paramagnetic resonance signal of Toac bound to the peptides, and Toac^Trp distances, estimated from the Toac fluorescence quenching of the Trp residue present in the peptides, indicate a more rigid and folded structure for the potent analogue as compared to the hormone, in aqueous medium. ß 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.

Collection of Czechoslovak Chemical Communications, 1992

A comparison of the CD spectra of MCH analogs differing in length but containing a heterodetic ri... more A comparison of the CD spectra of MCH analogs differing in length but containing a heterodetic ring of the same size (compounds I, IV and VII or III, VI and IX) reveals that a conformational change occurs upon elongating the peptide chain from thirteen to seventeen amino-acid residues. The 5-17 fragments appear to prefer a β-turn conformation, whereas the 1-17 full-sequence peptides prefer α-helical conformation. Peptides containing seventeen-membered ring exhibit greater conformational adaptability (the incorporation of their cyclic moiety into an ordered conformation being easier) than those containing a twenty-six-membered ring. Spectral properties of the twenty-three-membered heterodetic ring in peptides II and V indicate that they do not possess highly ordered conformation.

The adverse effects of tris (hydroxymethyl)-aminomethane (Tris) are for the first time reported o... more The adverse effects of tris (hydroxymethyl)-aminomethane (Tris) are for the first time reported on melanophore responses to agonists and potassium chloride. 2. Melanophore responses in Tris-or bicarbonate-buffered solutions were compared. 3. In the presence of Tris, the cumulative dose-response curve to norepinephrine was significantly shifted to the left. whereas methoxamine dose-response curves were similar in both buffers. 4. The percentage aggregation in response to synthetic MCH (melanin concentrating hormone) was not affected by Tris in the bathing medium. 5. The cumulative dose-response curve to potassium chloride was leftward shifted (one log case) in Tris-buffered solution. 6. These results suggest that in fish melanophore preparations Tris might exert its actions on the presynaptic membrane and/or on the synaptic cleft enzyme COMT, drawing on a greater availability of neurotransmitters at the melanophore membrane receptors.

analogue to vulgar vitiligo dermo-epidermal minigrafts 1Hospital Municipal Dr. Fernando Mauro Pir... more analogue to vulgar vitiligo dermo-epidermal minigrafts 1Hospital Municipal Dr. Fernando Mauro Pires da Rocha and

Brazilian Journal of Medical and Biological Research, 2012

Vertebrates have a central clock and also several peripheral clocks. Light responses might result... more Vertebrates have a central clock and also several peripheral clocks. Light responses might result from the integration of light signals by these clocks. The dermal melanophores of Xenopus laevis have a photoreceptor molecule denominated melanopsin (OPN4x). The mechanisms of the circadian clock involve positive and negative feedback. We hypothesize that these dermal melanophores also present peripheral clock characteristics. Using quantitative PCR, we analyzed the pattern of temporal expression of Opn4x and the clock genes Per1, Per2, Bmal1, and Clock in these cells subjected to a 14-h light:10-h dark (14L:10D) regime or constant darkness (DD). Also, in view of the physiological role of melatonin in the dermal melanophores of X. laevis, we determined whether melatonin modulates the expression of these clock genes. These genes show a time-dependent expression pattern when these cells are exposed to 14L:10D, which differs from the pattern observed under DD. Cells kept in DD for 5 days exhibited overall increased mRNA expression for Opn4x and Clock, and a lower expression for Per1, Per2, and Bmal1. When the cells were kept in DD for 5 days and treated with melatonin for 1 h, 24 h before extraction, the mRNA levels tended to decrease for Opn4x and Clock, did not change for Bmal1, and increased for Per1 and Per2 at different Zeitgeber times (ZT). Although these data are limited to one-day data collection, and therefore preliminary, we suggest that the dermal melanophores of X. laevis might have some characteristics of a peripheral clock, and that melatonin modulates, to a certain extent, melanopsin and clock gene expression.

Journal of Experimental Zoology, 1999

Skins of Potamotrygon reticulatus are light in color in vitro, exhibiting punctate melanophores. ... more Skins of Potamotrygon reticulatus are light in color in vitro, exhibiting punctate melanophores. Alpha-Melanocyte stimulating hormone (EC(50) = 4.58 x 10(-9) M) and prolactin (EC(50) = 1.44 x 10(-9) M) darken the skins in a dose-dependent manner. The endothelins ET-1, ET-2 and ET-3, and the purines, ATP, and uracil triphosphate (UTP) were not able to induce either skin lightening or darkening. Forskolin and the calcium ionophore A23187 promoted a dose-dependent darkening response, whereas N(2), 2'-O-dibutyryl guanosine 3'-5'-cyclic monophosphate (db cyclic GMP), phorbol-12-myristate-13-acetate (TPA), and 1-oleoyl-2-acetyl-sn-glycerol (OAG) were ineffective. The maximal response obtained with the calcium ionophore A23187 was only 76% of maximal darkening. These results indicate that the cyclic adenosine 3'-5'-monophosphate (cAMP) pathway is probably involved in the pigment dispersion of P. reticulatus melanophores. Other experiments should be done to further investigate how cytosolic calcium may be physiologically increased, and the existence of a putative cross-talk between calcium and cAMP signals. In conclusion, the only hormones effective on P. reticulatus melanophores were prolactin and alpha-MSH. No aggregating agent has been shown to antagonize these actions. Prolactin effect on elasmobranch melanophores adds a novel physiological role to this ancient hormone. J. Exp. Zool. 284:485-491, 1999.

Pigment Cell Research, 1989

Melanin concentrating hormone (MCH) is a cyclic heptadecapeptide, Asp-Thr-Met-Arg-Cys-Met-Val-Gly... more Melanin concentrating hormone (MCH) is a cyclic heptadecapeptide, Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val, synthesized in the hypothalamus and released by the neurohypophysis of teleost fish. This hormone is a potent lightening agent of fish skin. This lightening results from the stimulation of a centripetal melanosome (melanin granule) migration to a perinuclear position within integumental melanophores. MCH and related fragment analogues, MCHSi7 and MCH,-,, were used to investigate the ionic requirements for receptor activation by MCH on dermal melanophores of the fish Poecilia reticulntn. In calcium-free saline, the sensitivity of the melanophores to MCH and MCHi-14 increased, whereas the sensitivity of the cells to MCHS17 decreased. Verapamil diminished the sensitivity to MCHj17, but did not affect melanophore responses to MCH or MCHI-,,. The melanosome aggregating response to MCH was not affected in the presence of tetrodotoxin or in sodiumor potassium-free (choline-substituted) saline. These results suggest that neither TTX-sensitive sodium channels nor extracellular sodium or potassium ions play a role in MCH-induced melanosome aggregation. It is known that MCH and MCHl-L4 also exhibit MSH-like melanosome dispersion within melanophores, skin darkening activity on fish melanophores whereas MCHjl7 lacks this characteristic. Since the darkening activity of MCH and MCHI-11 requires calcium, these analogues exhibited a diminished lightening (MCHlike) activity in the presence of the divalent cation. In the absence of the Nterminal tetrapeptide sequence (necessary for the expression of MSH-like activity), a role for calcium on melanosome aggregation became evident. These results demonstrate a bifunctional role of calcium on melanosome movements.

Comparative Biochemistry and Physiology Part B: Comparative Biochemistry, 1992

1. Salmon melanin concentrating hormone (MCH) is a cyclic heptadecapeptide possessing the followi... more 1. Salmon melanin concentrating hormone (MCH) is a cyclic heptadecapeptide possessing the following primary structure: Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val. 2. In the fish, Synbranchus marmoratus, skin bioassay MCH5-15 is equipotent to MCH whereas MCH5-14, which comprises only the ring structure, is about 100-fold less active. 3. MCH and two fragment analogues, MCH5-15 and MCH5-14, were studied to determine their relative stability in the presence of fish serum and purified proteolytic enzymes, trypsin and alpha-chymotrypsin. 4. After 4 hr incubation in fish serum, MCH5-15 retained 1/100, MCH5-14 1/1000 and MCH only 6/1000 of the potency of the native hormone. 5. The three peptides were also very resistant to degradation by purified proteolytic enzymes involving the following relative order of resistance: MCH5-14 > MCH5-15 > MCH. MCH5-14 potency was not altered after a 1 hr incubation in either enzyme whereas MCH retained 1/10 and 4/100 of its original potency, and MCH5-15 retained 1/10 and 8/10 of its original potency, after 1 hr in trypsin and alpha-chymotrypsin, respectively.

Anais da Academia Brasileira de Ciências, 1985

We report here the effects of cytochalasin B, colchicine and vinblastine on melanosome migration ... more We report here the effects of cytochalasin B, colchicine and vinblastine on melanosome migration in Papiliochromis ramirezi melanophores. Melanosome migration was not affected by 2 X 10(-5) M cytochalasin B. On the other hand, the aggregation, usually elicited by 10(-6) M norepinephrine, was completely inhibited by simultaneous treatment with 10(-3) M colchicine and cold (0-3 degrees C). Same results were obtained with 10(-3) M vinblastine. Lower concentrations of colchicine had no effect on granule aggregation. However, the aggregation in 50% of the melanophores was still blocked by 10(-5) M vinblastine, whereas 10(-7) M vinblastine was ineffective. Melanosome dispersion usually elicited by 10(-3) M theophylline was significantly accelerated by 10(-3) M colchicine, but delayed by 10(-3) M vinblastine. Lower concentrations of both agents had no effect on pigment dispersion. Therefore our results strongly suggest that microtubule structural integrity is essential to P. ramirezi melan...

Progress in clinical and biological research, 1988

Comparative Biochemistry and Physiology Part C: Comparative Pharmacology, 1991

Beneficial cutaneous bacteria on amphibians can protect against the lethal disease chytridiomycos... more Beneficial cutaneous bacteria on amphibians can protect against the lethal disease chytridiomycosis, which has devastated many amphibian species and is caused by the fungus Batrachochytrium dendrobatidis. We describe the diversity of bacteria on red-backed salamanders (Plethodon cinereus) in the wild and the stability of these communities through time in captivity using cultureindependent Illumina 16S rRNA gene sequencing. After field sampling, salamanders were housed with soil from the field or sterile media. The captive conditions led to different trajectories of bacterial communities. Eight OTUs present on 490% of salamanders in the field, through time, and in both treatments were defined as the core community, suggesting that some bacteria are closely associated with the host and are independent of an environmental reservoir. One of these taxa, a Pseudomonas sp., was previously cultured from amphibians and found to be antifungal. As all host-associated bacteria were found in the soil reservoir, environmental microbes strongly influence host-microbial diversity and likely regulate the core community. Using PICRUSt, an exploratory bioinformatics tool to predict gene functions, we found that core skin bacteria provided similar gene functions to the entire community. We suggest that future experiments focus on testing whether core bacteria on salamander skin contribute to the observed resistance to chytridiomycosis in this species even under hygenic captive conditions. For disease-susceptible hosts, providing an environmental reservoir with defensive bacteria in captive-rearing programs may improve outcomes by increasing bacterial diversity on threatened amphibians or increasing the likelihood that defensive bacteria are available for colonization.

Journal of Experimental Zoology, 1999

Total serum IgM levels were studied in 84 mothers of infants with group-B streptococcal (GBS) sep... more Total serum IgM levels were studied in 84 mothers of infants with group-B streptococcal (GBS) septicemia/meningitis and compared to IgM concentrations in 91 parturients who were urogenital carriers of GBS but nevertheless gave birth to healthy infants. In all, 22 (27%) in the study group showed IgM levels above the arbitrarily selected limit of 2.40 g/1, in contrast to 12 (13%) of 91 controls (p = 0.02). Among the study group members whose infants were infected with GBS type III, 8 of 34 (24%) were high in serum IgM, com pared to only 2 of 34 (6%) of the corresponding controls (p = 0.04). The total serum IgG levels did not differ be tween the two groups.

Comparative Biochemistry and Physiology Part C: Comparative Pharmacology, 1984

Pigment Cell Research, 1990

An in vitro crustacean (freshwater shrimp, Macrobrachiurn potiuna) erythrophore bioassay for chro... more An in vitro crustacean (freshwater shrimp, Macrobrachiurn potiuna) erythrophore bioassay for chromatophorotropins and other pigment cell agonists is described. The present assay is a quantitative method that determines the pigment responses with the aid of an ocular micrometer. The pigment granules within the erythrophores are dispersed out into the dendritic processes of the cells when the isolated carapace is placed in physiological solution. This bioassay provides, therefore, a method for measuring the response of the pigment cells to aggregating agents such as pigment concentrating hormone (PCH). This bioassay is sensitive to PCH at a concentration as low as 3 x 10-12M. Calcium ionophore A23187 mimics the actions of PCH, but, unlike the hormone, the ionophoreinduced pigment aggregation is irreversible after physiological solution rinses. Therefore, chromatophorotropic activities of pigment dispersing agents, such as pigment dispersing hormones (PDH), can be determined on ionophore-treated erythrophores. The potencies of a-PDH and p-PDH show a threefold difference (not significant). Because of its convenience and its ability to make an objective determination of the bidirectional pigment movements within erythrophores, this bioassay is a suitable method for further structure-activity studies of the various chromatophorotropins and their analogs.

Pigment Cell Research, 1990

Norepinephrine (NE) and phenylephrine (Phe) were employed to study the ionic requirements for alp... more Norepinephrine (NE) and phenylephrine (Phe) were employed to study the ionic requirements for alpha adrenoceptor activation in the teleost Poeciliu reticulutu melanophores. As expected the beta adrenoceptor blocker, propranolol, increased the sensitivity of the preparation to NE (5.8 times), and was therefore employed in all the experimental procedures. Neither cocaine (a neuronal uptake blocker) nor dexamethasone (an extraneuronal uptake blocker) enhanced the sensitivity of the preparation to NE, suggesting that these inactivating mechanisms would not play a role in P. reticulutu pigmentary system. However, in the absence of calcium, the dose-response curve (DRC) to NE was displaced to the left about 3.5 times, whereas the DRC to Phe was not affected. These results indicate that a neuronal uptake is active, but was not demonstrated by the classical pharmacological tools, probably due to an assymmetric display of the nervous endings. The DRC to NE was rightward displaced (14.1 times) in the presence of the calcium channel blocker Verapamil, whereas the DRC to Phe was not affected. These data suggest that P. reticulutu melanophores possess a mixed population of alphal and alphaz adrenoceptors, the activation of the latter eliciting an extracellular calcium influx. In sodium-free saline, the DRC to NE was rightward shifted (6.6 times) and the response to Phe was impaired in such a way that the maximal response was not achieved. The DRC to both NE and Phe were rightward displaced (7.9 and 2.7 times respectively) in the presence of the sodium channel blocker tetrodotoxin (TTX) 10-'M. In potassium-free saline, the melanophore sensitivity to Phe was increased, whereas the responses to NE were not affected, suggesting a differential sensitivity of the two alpha adrenoceptor subtypes to the resulting membrane hyperpolarization. Based on the literature and on our data we propose that P. reticulutu melanophores possess a mixed population of alphal and alphaz receptors. The activation of both subtypes of alpha adrenoceptors elicits a Na+ ion influx through TTX-sensitive sodium channels. The stimulation of alpha, adrenoceptors also requires an extracellular calcium influx, through the opening of slow calcium channels.

Mini-Reviews in Medicinal Chemistry, 2005

Medicinal Chemistry, 2008

In vivo and in vitro assays were performed with S91 murine melanoma cells aiming to investigate t... more In vivo and in vitro assays were performed with S91 murine melanoma cells aiming to investigate the effects of testosterone and photoperiod on tumor growth and melanogenesis (tyrosinase activity). In vivo assays were performed by inducing melanoma tumors in castrated mice receiving increasing concentrations of testosterone and submitted to varying photoperiod regimens. The results demonstrated that the increase of melanin content was higher in animals submitted to the longest days, thus demonstrating the importance of photoperiod length in melanin synthesis. Increase in tumor growth and protein content was observed in testosterone-treated animals submitted to 12L:12D; in testosterone-treated animals submitted to 4L:20D and 20L:4D tumor growth was significantly smaller. In S91 cultured cells, testosterone increased cell proliferation and reduced tyrosinase activity in a dose-dependent manner. Radioactive binding assays demonstrated that the hormone was acting through low affinity testosterone receptors, since the presence of aromatase inhibitor did not affect the binding assay in a statistically significant way, and all the in vitro experiments were performed in the presence of the inhibitor. Our in vivo data added to the in vitro results corroborate the hypothesis that S91 melanoma cells directly respond to testosterone and that this effect is modulated by light.

Life Sciences, 1987

H-Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val-OH , melanin concentrating ... more H-Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val-OH , melanin concentrating hormone (MCH), exhibits both melanin granule concentrating and dispersing (MSH-like) activities. Fragment analogues of MCH were synthesized as described herein and the melanotropic activities of the peptides were determined. In the frog (Rana pipiens) and lizard (Anolis carolinensis) skin bioassays, the 5-17 and 5-14 fragments of MCH were inactive (at concentrations of 10(-5)M or less), whereas the 1-14 sequence exhibited minimal (about 10%) MSH-like activity compared to MCH, which, as reported previously, was about 600 times less active than alpha-MSH. In the teleost (fish) skin bioassay, the MCH5-17 analogue was equipotent to MCH, whereas the 1-14 analogue was 10-30 times and the cyclic N- and C- terminal truncated analogue, MCH5-14, was about 300 times less active than MCH. These results suggest that the N-terminal sequence is particularly critical to MSH-like activity in the tetrapod species studied, whereas other structural regions of MCH, particularly in the C-terminal, are more related to MCH activity in teleosts.

General and Comparative Endocrinology, 2008

Insulin is the hormone that plays an essential role in metabolism and mitosis of normal and tumor... more Insulin is the hormone that plays an essential role in metabolism and mitosis of normal and tumor cells, exerting its pleiotropic effects through binding to specific membrane receptors and promoting the phosphorylation of tyrosine residues of the receptor itself and of other components of the signaling pathway. The aim of this study was to investigate the effects of insulin on melanogenesis and cell growth in three different cell lines: the goldfish GEM-81 erythrophoroma cells (undifferentiated and differentiated with 1.5% dimethylsulfoxide-DMSO), and the murine B16F10 and Cloudman S91 melanoma cells. Undifferentiated GEM-81 and B16F10 cells responded to insulin with a small increase of cell proliferation, whereas S91 cells responded with a decrease of growth. In the two mammalian cell lines, and in DMSO-differentiated GEM-81 cells, the hormone strongly inhibited melanogenesis, by decreasing tyrosinase activity. In undifferentiated GEM-81 cells, insulin had no effect on tyrosinase activity. An increase in the tyrosine phosphorylation status of pp185 (insulin receptor substrate 1 and 2-IRS-1/2) phosphorylation degree was observed in S91 mouse melanoma and in differentiated GEM-81 erythrophoroma cells, suggesting that this specific protein was maintained during transformation process and participates in insulin signaling. Our results imply an ancient and diverse history of the insulin signaling system in vertebrate pigment cells.

FEBS Letters, 2001

Similar to melanocyte stimulating hormone (K K-MSH), its potent and long-acting analogue, [Nle 4 ... more Similar to melanocyte stimulating hormone (K K-MSH), its potent and long-acting analogue, [Nle 4 , D-Phe 7 ]K K-MSH, when labeled with the paramagnetic amino acid probe 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid (Toac), maintains its full biological potency, thus validating any comparative structural investigations between the two labeled peptides. Correlation times, calculated from the electron paramagnetic resonance signal of Toac bound to the peptides, and Toac^Trp distances, estimated from the Toac fluorescence quenching of the Trp residue present in the peptides, indicate a more rigid and folded structure for the potent analogue as compared to the hormone, in aqueous medium. ß 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.

Collection of Czechoslovak Chemical Communications, 1992

A comparison of the CD spectra of MCH analogs differing in length but containing a heterodetic ri... more A comparison of the CD spectra of MCH analogs differing in length but containing a heterodetic ring of the same size (compounds I, IV and VII or III, VI and IX) reveals that a conformational change occurs upon elongating the peptide chain from thirteen to seventeen amino-acid residues. The 5-17 fragments appear to prefer a β-turn conformation, whereas the 1-17 full-sequence peptides prefer α-helical conformation. Peptides containing seventeen-membered ring exhibit greater conformational adaptability (the incorporation of their cyclic moiety into an ordered conformation being easier) than those containing a twenty-six-membered ring. Spectral properties of the twenty-three-membered heterodetic ring in peptides II and V indicate that they do not possess highly ordered conformation.