Post by Max on Jun 12, 2005 18:55:22 GMT -5
(Ro)accutane induced signicicant inhibition of serotonergic biosynthesis in human subjects: Suggested significant inhibition of the tryptophan hydroxylase (TPH) through decreased promoter activity due to Sp1 and NF-Y dephosphorylation leading to decreased binding affinity and formation of Sp proteins, partially through significant elevation of alkaline phosphatases
Tryptophan hydroxylase (TPH) catalyses the rate-limiting reaction in the biosynthesis of serotonin. In humans, two different TPH genes exist, located on chromosomes 11 and 12, respectively, and encoding two enzymes (TPH1 and TPH2) with an overall sequence identity of 71% [1]. In rats nuclear transcription factor Y (NF-Y) is found to regulate TPH [2]and in rats, retinoic acid has found to be one factor that modulates NF-Y [3].
In human pinealocytes, NF-Y and Sp1 transactivators bind the inverted CCAAT box and GC-rich-region in the TPH gene, respectively [4]. Transcription of a 2.1-kb fragment of the human TPH promoter is induced by cAMP, although it lacks the canonical cAMP responsive element, CRE. An additional cis -acting sequence, the adjacent GC-rich region, cooperates with the inverted CCAAT box for the full activation of basal transcription, and both elements are essential for the full cAMP response. In small doses, retinoids induce the Retinoid receptors RARs/RXRs and physically interact with Sp1, potentiate Sp1 binding to the GC box motifs [5]. Unfortunately no publicly available study shows how NF-Y, Sp1 or its binding sites (GC box motifs) are affected by a dose of retinoic acid beyond the physiological limit. However an increased alkaline phosphatase as found in subjects exposed to (Ro)accutane, and is even admitted by Hoffman la Roche itself [0 and more] is found to dephosphorylate Sp proteins [6], which most likely leads to a significantly decreased promotion of the TPH-gene and lessened biosynthesis of serotonin. Further evidence for a dramatically reduced Sp promotion comes with the findings of dramatically increased homocysteine (Hcy) levels in subjects exposed to (Ro)accutane [0 and more]. Cystathionine beta-synthase (CBS) catalyzes the condensation of serine and homocysteine to form cystathionine, and is promoted by Sp1 and Sp3 [7] in a similiar manner to how the TPH gene is promoted.
In human NT2 cells, formation of the Sp1/Sp3 containing complex was inhibited by anti-RA receptor (RAR) antibodies [8]. This is probably due to a lessened promotion of Sp1, and a low degree of phosphorylation. Exposure of extremely high doses of retinoic acid, (Ro)accutane, in human acne-subjects, and thus inhibition of Sp1/Sp3 is highly likely due to inhibition of binding through high dose inhibition of phosphorylation. A bell shaped curve of Sp1 binding and activity is likely.
Inhibition of serotonerg 5HT(1A) receptor expression and inhibtion of glycine responses through inhibition of several protein kinases and inhibition of phosphorylation of Sp1
The somatodendritic 5-HT(1A) autoreceptor has been considered a major determinant of the output of the serotonin (5-HT) neuronal system. 5-HT autoinhibition is critically regulated by the tryptophan hydroxylase-activating kinases calcium/calmodulin protein kinase II (CaMKII) and protein kinase A (PKA) [9]. The expression level of the 5-HT(1A) receptor gene (htr1a) in the central nervous system (CNS) is implicated in the aetiology and treatment of anxiety disorders and depression. In mice, htr1a have revealed that its proximal promoter is GC rich and TATA-less. Several functional transcription factor binding sites, including MAZ and SP1 recognition sequences, have been identified [10]. It is shown that inhibition of Sp1 phosphorylation causes a decreased binding affitnity for the transcription on promoter activity. Since the Sp1 is found to be a 5HT(1A) promoter, the receptor expression is here suggested to be significantly decreased.
Mammalian alkaline phosphatases (AP) are glycosylphosphatidylinositol (GPI) anchored proteins that are localized on the outer layer of the plasma membrane. The GPI anchors are covalently attached to the C-termini of proteins and consist of a glycan chain bonded to phosphatidylinositol with two acyl chains anchored into the membrane bilayer [11]. In the the rat hippocampus, exposure to alkaline phosphatase and inhibition of PKC is found to inhibit glycine responses, which is affecting the serotonerg 5-HT receptors. PKC was found to be involved in the modulation of hippocampal glycine receptors, since the observed effect was more prominent when the phorbol ester PMA, an activator of PKC, was added [12]. In 10T1/2 cells, a decrease of total PKC activity was observed following exposure to 10(-5) M 13-cis-retinoic acid [13]. Inhibition of PKC is likely affecting many cell lines, including cell lines in the brain, and is suggested to logically result in inhibition of glycine responses, as well as lack of phosphorylation of Sp1 and NF-Y and thus promoter activity.
Serotonerg transport
1) Human serotonin transporter (hSERT) and AP-2
Retinoids activate AP2 transcription factors [14 and more]. Transcription factor AP-2 is essential for neuronal development and many genes involved in the brainstem monoaminergic systems have binding sites for AP-2 in their regulatory regions. The genotype of the AP-2beta isoform has been associated with e.g. anxiety-related personality traits and with platelet MAO activity [15].
Exon 1B of the human serotin transporter (hSERT) is surrounded by several elements potentially suitable for regulating serotonin transporter gene expression in vivo, including consensus sites for transcription factors AP-1, AP-2, CREB/ATF, and NF-kappaB [17]. All of these having in different studies been found to be significantly modultated by retinoic acid.
2) 5HTT
In humans, integrin beta 3 (ITGB3) is found to affect the serotonin transporter gene (5HTT) [18]. 1,25-dihydroxyvitamin D3 (D3) is found to accelerate beta 3 transcription, and avian beta 3 promoter is suggested to contain a vitamin D response element (VDRE) [19]. A significant fall in metabolites of 1,25-dihydroxyvitamin D3 were found to in acne-subjects during and post (Ro)accutane exposure in repeated studies [20 and more]. In raphe serotonergic neurons, a TATA-like motif and several potential binding sites for transcription factors, including two AP1, several AP2 and AP4 binding sites, CCAAT and GC boxes was found in the 5-HTT promoter[21].
An impaired function of serotonin transporter gene(5HTT) through alterations in the promoter region and decreased 1,25 dihyrdoxyvitamin D3, as a direct consequence of (Ro)accutane exposure is here suggested.
(Ro)accutane induced inhibition of androgen receptors is suggested to be modulatory of 5-HT activity
Inhibition of androgen receptors is suggested to result in an alteration in tryptophan residues, a precursor amino acid to serotonin. Binding to both types of DNA response element resulted in changes in the intrinsic fluorescence emission spectrum for four tryptophan residues within the AR-NTD and resulted in a more protease-resistant conformation [22].
Inhibition of insulin transport to the brain, suggested to futher decrease 5-HT receptor activity
The Hoffman la Roche corporation itself, salesagent of (Ro)accutane, has admitted to the finding of an increased alkaline phosphatase in acne-subjects exposed to the toxin [0]. A positive correlation between ecto-ALP activity and (125)I-insulin incorporation (r = 0.82; P < 0.0001) was shown in cultured rat brain endothelial cells, suggesting that insulin entry into the blood-brain barrier may be modulated through ALP [23]. A close connection between 5-HT activity in the brain and peripheral sensitivity to insulin has been suggested[24].
Six weeks of isotretinoin exposure caused a statistically significant 19% increase in suction blister fluid TGF-beta1 [4].
TPH-1 location: 11p15.1 (genatlas)
Tryptophan hydroxylase (TPH) catalyses the rate-limiting reaction in the biosynthesis of serotonin. In humans, two different TPH genes exist, located on chromosomes 11 and 12, respectively, and encoding two enzymes (TPH1 and TPH2) with an overall sequence identity of 71% [1]. In rats nuclear transcription factor Y (NF-Y) is found to regulate TPH [2]and in rats, retinoic acid has found to be one factor that modulates NF-Y [3].
In human pinealocytes, NF-Y and Sp1 transactivators bind the inverted CCAAT box and GC-rich-region in the TPH gene, respectively [4]. Transcription of a 2.1-kb fragment of the human TPH promoter is induced by cAMP, although it lacks the canonical cAMP responsive element, CRE. An additional cis -acting sequence, the adjacent GC-rich region, cooperates with the inverted CCAAT box for the full activation of basal transcription, and both elements are essential for the full cAMP response. In small doses, retinoids induce the Retinoid receptors RARs/RXRs and physically interact with Sp1, potentiate Sp1 binding to the GC box motifs [5]. Unfortunately no publicly available study shows how NF-Y, Sp1 or its binding sites (GC box motifs) are affected by a dose of retinoic acid beyond the physiological limit. However an increased alkaline phosphatase as found in subjects exposed to (Ro)accutane, and is even admitted by Hoffman la Roche itself [0 and more] is found to dephosphorylate Sp proteins [6], which most likely leads to a significantly decreased promotion of the TPH-gene and lessened biosynthesis of serotonin. Further evidence for a dramatically reduced Sp promotion comes with the findings of dramatically increased homocysteine (Hcy) levels in subjects exposed to (Ro)accutane [0 and more]. Cystathionine beta-synthase (CBS) catalyzes the condensation of serine and homocysteine to form cystathionine, and is promoted by Sp1 and Sp3 [7] in a similiar manner to how the TPH gene is promoted.
In human NT2 cells, formation of the Sp1/Sp3 containing complex was inhibited by anti-RA receptor (RAR) antibodies [8]. This is probably due to a lessened promotion of Sp1, and a low degree of phosphorylation. Exposure of extremely high doses of retinoic acid, (Ro)accutane, in human acne-subjects, and thus inhibition of Sp1/Sp3 is highly likely due to inhibition of binding through high dose inhibition of phosphorylation. A bell shaped curve of Sp1 binding and activity is likely.
Inhibition of serotonerg 5HT(1A) receptor expression and inhibtion of glycine responses through inhibition of several protein kinases and inhibition of phosphorylation of Sp1
The somatodendritic 5-HT(1A) autoreceptor has been considered a major determinant of the output of the serotonin (5-HT) neuronal system. 5-HT autoinhibition is critically regulated by the tryptophan hydroxylase-activating kinases calcium/calmodulin protein kinase II (CaMKII) and protein kinase A (PKA) [9]. The expression level of the 5-HT(1A) receptor gene (htr1a) in the central nervous system (CNS) is implicated in the aetiology and treatment of anxiety disorders and depression. In mice, htr1a have revealed that its proximal promoter is GC rich and TATA-less. Several functional transcription factor binding sites, including MAZ and SP1 recognition sequences, have been identified [10]. It is shown that inhibition of Sp1 phosphorylation causes a decreased binding affitnity for the transcription on promoter activity. Since the Sp1 is found to be a 5HT(1A) promoter, the receptor expression is here suggested to be significantly decreased.
Mammalian alkaline phosphatases (AP) are glycosylphosphatidylinositol (GPI) anchored proteins that are localized on the outer layer of the plasma membrane. The GPI anchors are covalently attached to the C-termini of proteins and consist of a glycan chain bonded to phosphatidylinositol with two acyl chains anchored into the membrane bilayer [11]. In the the rat hippocampus, exposure to alkaline phosphatase and inhibition of PKC is found to inhibit glycine responses, which is affecting the serotonerg 5-HT receptors. PKC was found to be involved in the modulation of hippocampal glycine receptors, since the observed effect was more prominent when the phorbol ester PMA, an activator of PKC, was added [12]. In 10T1/2 cells, a decrease of total PKC activity was observed following exposure to 10(-5) M 13-cis-retinoic acid [13]. Inhibition of PKC is likely affecting many cell lines, including cell lines in the brain, and is suggested to logically result in inhibition of glycine responses, as well as lack of phosphorylation of Sp1 and NF-Y and thus promoter activity.
Serotonerg transport
1) Human serotonin transporter (hSERT) and AP-2
Retinoids activate AP2 transcription factors [14 and more]. Transcription factor AP-2 is essential for neuronal development and many genes involved in the brainstem monoaminergic systems have binding sites for AP-2 in their regulatory regions. The genotype of the AP-2beta isoform has been associated with e.g. anxiety-related personality traits and with platelet MAO activity [15].
Exon 1B of the human serotin transporter (hSERT) is surrounded by several elements potentially suitable for regulating serotonin transporter gene expression in vivo, including consensus sites for transcription factors AP-1, AP-2, CREB/ATF, and NF-kappaB [17]. All of these having in different studies been found to be significantly modultated by retinoic acid.
2) 5HTT
In humans, integrin beta 3 (ITGB3) is found to affect the serotonin transporter gene (5HTT) [18]. 1,25-dihydroxyvitamin D3 (D3) is found to accelerate beta 3 transcription, and avian beta 3 promoter is suggested to contain a vitamin D response element (VDRE) [19]. A significant fall in metabolites of 1,25-dihydroxyvitamin D3 were found to in acne-subjects during and post (Ro)accutane exposure in repeated studies [20 and more]. In raphe serotonergic neurons, a TATA-like motif and several potential binding sites for transcription factors, including two AP1, several AP2 and AP4 binding sites, CCAAT and GC boxes was found in the 5-HTT promoter[21].
An impaired function of serotonin transporter gene(5HTT) through alterations in the promoter region and decreased 1,25 dihyrdoxyvitamin D3, as a direct consequence of (Ro)accutane exposure is here suggested.
(Ro)accutane induced inhibition of androgen receptors is suggested to be modulatory of 5-HT activity
Inhibition of androgen receptors is suggested to result in an alteration in tryptophan residues, a precursor amino acid to serotonin. Binding to both types of DNA response element resulted in changes in the intrinsic fluorescence emission spectrum for four tryptophan residues within the AR-NTD and resulted in a more protease-resistant conformation [22].
Inhibition of insulin transport to the brain, suggested to futher decrease 5-HT receptor activity
The Hoffman la Roche corporation itself, salesagent of (Ro)accutane, has admitted to the finding of an increased alkaline phosphatase in acne-subjects exposed to the toxin [0]. A positive correlation between ecto-ALP activity and (125)I-insulin incorporation (r = 0.82; P < 0.0001) was shown in cultured rat brain endothelial cells, suggesting that insulin entry into the blood-brain barrier may be modulated through ALP [23]. A close connection between 5-HT activity in the brain and peripheral sensitivity to insulin has been suggested[24].
Six weeks of isotretinoin exposure caused a statistically significant 19% increase in suction blister fluid TGF-beta1 [4].
TPH-1 location: 11p15.1 (genatlas)