Is the cyclic AMP in psoriatic epidermis low?

Serum lactate dehydrogenase level as a possible predictor of treatment preference in psoriasis

BACKGROUND

The efficacy of small molecule inhibitors for intracellular signal mediators varies among the individuals, and their mechanism of action is broad. A phosphodiesterase 4 inhibitor apremilast shows a dramatic effect on a certain proportion of psoriatic patients by modulating the cellular metabolism and regulating the production of pro-inflammatory molecules. However, it is unclear to which disease subtype this drug benefits. While psoriasis is a Th17-mediated disease, how immune cells are affected by the modulation of cellular metabolism is not fully evaluated, either.

OBJECTIVE

This study aims to identify the indices which predict the efficacy of apremilast in psoriasis, and to investigate the impact of metabolic activity in immune cells on the psoriatic pathogenesis.

METHODS

The association of treatment efficacy with clinical and laboratory data of the 58 psoriatic patients was evaluated. The reflector of the associated index was also sought among the indices of cellular metabolic pathways by use of an extracellular flux analyzer.

RESULTS

There was a correlation between clinical improvement and the serum lactate dehydrogenase (LDH) level in the patients treated with apremilast but not in those with biologics. Serum LDH level did not correlate with the cutaneous disease severity but correlated with the oxygen consumption rate of blood T cells.

CONCLUSION

Psoriatic patients with high serum LDH level can be benefitted by apremilast. The serum LDH level reflects the augmented respiratory activity of T cells in psoriasis. Our results would highlight the importance of regarding metabolic skew in immune cells as a treatment target in psoriasis.

Soluble adenylyl cyclase defines a nuclear cAMP microdomain in keratinocyte hyperproliferative skin diseases

Cyclic adenosine monophosphate (cAMP) is a nearly ubiquitous signaling molecule important for numerous signaling pathways in human skin. We studied a novel class of mammalian adenylyl cyclase, the soluble adenylyl cyclase (sAC). We examined sAC localization in normal human skin and found it to be present in keratinocytes, melanocytes, mononuclear cells, eccrine ducts, and nerves. In normal skin, sAC keratinocyte staining was evenly distributed throughout the cell. However, in certain hyperproliferative disorders of the skin, including psoriasis, verruca vulgaris, and SCCIS on sun-damaged skin, sAC keratinocyte staining was predominantly nuclear. In contrast, in other hyperproliferative disorders, such as basal cell carcinoma, sAC staining was similar to normal human skin. Using a model of epithelial differentiation, we established that sAC migrates into the nucleus when differentiated cells are induced to reenter the cell cycle. Previous work had determined that nuclear sAC activates the cAMP-response-element-binding (CREB) transcription factor, and we found that in psoriasis lesions, nuclear sAC occurs concomitantly with activation of CREB. Hence, sAC may play a role in the pathogenesis of certain hyperproliferative skin disorders via modulation of gene expression.

Three decades of psoriasis research: where has it led us?

Psoriasis is a common chronic skin disease. Its pathogenesis has intensively been investigated in the last 3 decades. In the 1970s, the observed increased proliferation of keratinocytes and their altered differentiation were considered to be the most important signs and causes of psoriatic skin lesions. Since the early 1980s, T cells slid into the focus of psoriasis research. It was then postulated that a subpopulation of T cells, so-called T1 cells, and their prominent cytokine interferon-gamma, had a dominant role in the pathogenesis of psoriasis. In the last decade, new data regarding macrophages and dendritic cells and the high therapeutic success of anti-tumor necrosis factor alpha biologics led to the assumption that antigen-presenting cells are important not only in the induction of psoriasis but also in its maintenance. The knowledge gained over the past 3 decades let us postulate that psoriasis is an immunologically induced, overshot, regeneration-like reaction of the skin in which various cells play a dominant role at different stages. This hypothesis is also supported by the very recent discoveries about interleukin (IL)-22, IL-20, and IL-23.

A deficient function of the antioxidative system of the organism as an aetiopathogenetic factor in psoriasis

The main idea of a new hypothesis about the aetiopathogenesis of psoriasis concerns the significance of interrelation between pro- and antioxidants, vitamin A-dependent keratin synthesis and proliferation of keratinocytes. On the basis of postulated deregulation in the antioxidative system of the organism, we explain the predisposition, the initiation and pathogenesis of lesions, their persistence and resolution and the operation mechanisms of antipsoriatics.

"Ischemic" rise of epidermal cyclic AMP is a beta-adrenergic adenylate cyclase-dependent process

The endogenous level of epidermal cyclic AMP does not remain constant but increases rapidly and transiently after removal of the tissue; this is known as the "ischemia" effect. UVB-irradiated epidermis which shows increased beta-adrenergic response revealed an increased ischemia effect, while psoriatic involved epidermis which shows decreased beta-adrenergic response revealed a decreased ischemia effect. Because of the similar rise-and-fall pattern between the ischemia effect and the beta-adrenergic response, the mechanism of the ischemia effect was investigated, especially in terms of the beta-adrenergic relationship. The ischemic rise of epidermal cyclic AMP was well preserved after 6 h pretreatment at 4 degrees C, and, following the pretreatment, the skin markedly increased its cyclic AMP level by the 37 degrees C treatment with 1 mM isobutylmethyl xanthine. The addition of propranolol or cimetidine at the time of 37 degrees C treatment (following the 4 degrees C pretreatment) had no effect on the ischemia effect; both skin groups markedly increased their cyclic AMP levels to an extent similar to that of the control skin. However, the addition of propranolol at the time of both preincubation (at 4 degrees C) and incubation (at 37 degrees C) markedly decreased the ischemic rise of cyclic AMP. Similar treatment by cimetidine had no effect on the ischemia effect. There was no significant difference in cyclic AMP phosphodiesterase activities among skin groups by propranolol or cimetidine pretreatment. These results indicate that the so-called ischemic rise of epidermal cyclic AMP is actually the beta-adrenergic adenylate cyclase-dependent process. Our results also indicate that the magnitude of the "ischemic" rise of cyclic AMP is generally parallel to the beta-adrenergic responsiveness of epidermis.

Cyclic AMP-dependent protein kinase isozymes of pig skin and human skin from normal and psoriatic subjects

Cyclic AMP-dependent protein kinase isozymes of pig and human skin (epidermis) were separated by DEAE-cellulose column chromatography after micromodification for small biopsy samples. Clear-cut separations of type I and type II isozymes, which were of about equal amounts, could be obtained only when the ischemia effect was avoided by in vivo freezing of skin and homogenization for less than 10 s. Intradermal injections of epinephrine caused dose-dependent activation of type I isozyme, but not of type II. Injections of other skin adenylate cyclase stimulators such as histamine, adenosine, and prostaglandin E2 elevated the local cyclic AMP levels to not more than 5 pmol/mg protein and also stimulated only the type I isozyme. Incubation of keratome-sliced pig skin under various conditions caused both activation by dissociation and inactivation by reassociation of the subunits, which appeared to be dependent on the cyclic AMP content. Epinephrine added to the incubation medium led to complete activation of both type I and type II isozymes (the intraepidermal cyclic AMP contents ranged from 20-50 pmol/mg protein). The isozymes of normal skin and involved skin of psoriatics showed identical peaks of type I and type II isozymes of equal amounts. The data indicate that protein kinase in the involved skin is not in an activated (by cyclic AMP) state.

Measurement of adenosine 3',5'-monophosphate-dependent protein kinase and phosphorylase activities in in vivo conditions

Microassay procedures for cAMP-dependent protein kinase and phosphorylase were developed which detected these activities in less than 25 micrograms of frozen-dried epidermis from a punch biopsy of skin without homogenization. Using these procedures, the activation of cAMP-dependent protein kinase and phosphorylase by beta-adrenergic stimulation in mouse skin was studied in vivo. Cyclic AMP-dependent protein kinase was stimulated by isoproterenol and inhibited by propranolol. Isoproterenol stimulation also activated phosphorylase a in mouse skin. In normal epidermis and uninvolved and involved epidermis from psoriatic patients no significant differences were found in the activities of cAMP-dependent kinase and phosphorylase a. In all experiments we observed that the unstimulated activity ratios of phosphorylase a/total phosphorylase were around 20-30%; these values were much lower than those hitherto reported and show a preponderance of phosphorylase b rather than a. We suggest that in previous reports where phosphorylase a domination was found, phosphorylase b to a activation occurred during homogenization. The data also suggest that in the steady state no obvious defect in basic activities of cAMP-dependent protein kinase and phosphorylase is observed in psoriatic skin.

Immunohistochemical localization of cyclic nucleotides in guinea pig lip

The cellular localization of cAMP and cGMP in the guinea pig lip was investigated with an indirect immunofluorescence technique. cAMP was distributed both in cell membranes and cytoplasmic elements with coarse and granular intranuclear fluorescence, while cGMP was localized in nuclear sites including nuclear membranes as well as cell membranes and cytoplasm. In the basal portion, both cAMP and cGMP fluorescence was weaker in cytoplasm and cell membranes than seen in the upper portion.

Effect of phorbol ester application and other mitogenic treatments on 3',5'-cyclic-nucleotide phosphodiesterase activity in mouse epidermis in vivo

The effects of phorbol ester application and of other mitogenic treatments on the activity of 3',5'-cyclic-nucleotide phosphodiesterase were investigated in dorsal mouse epidermis in vivo. Local treatment with either the weak tumor promoter phorbol 12,13-dibenzoate or the strong promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) increased the activity of the high affinity enzyme (Km = 4 microM). The enzymic changes began within the first hour after application, and lasted for about 5 days. maximal stimulations of approximately 300--400% were reached after 3--6 h with TPA application, whereas with phorbol dibenzoate the maximum could only be reached after 1--2 days. TPA stimulation of the enzyme depended on doses within the range of 0.2 to 20 nmol and could be completely prevented by cycloheximide, but not by 5-azacytidine, actinomycin D, 5,8,11,14-eicosatetraynoic acid or indomethacin. No evidence could be found for cAMP participation in enzyme induction. An increase in enzyme activity could also be observed after other mitogenic treatments such as local application of the weakly promoting phorbol esters C14:4-phorbol acetate ("Ti8") and 4.O-methyl-TPA, or of the non-promoting divalent cation ionophore A 23187, as well as after treatment with a depilatory cream. Skin massage or removal of the horny layer, which also stimulate mitosis, did not evoke a significant increase in enzyme activity. No apparent correlation exists between the hyperplasiogenic and tumor-promoting effectiveness of a manipulation and its effect on epidermal 3',5'-cyclic-nucleotide phosphodiesterase.

The effect of steroid and dithranol therapy on cyclic nucleotides in psoriatic epidermis

Absolute values of both cAMP and cGMP leves were measured in the involved and uninvolved skin of psoriatic patients, and also the effect of topical therapy on these levels in the involved skin was studied. The mean cGMP level in the untreated psoriatic plaque was increased by 300% compared to the non-involved skin (which did not differ from normal skin), but no significant difference in cAMP levels was found. Epidermal stripping of uninvolved skin, which stimulates cell proliferation, did not change the cGMP level. Treatment of the psoriasis with dithranol caused the cGMP levels to return to normal, but a potent topical glucocorticoid, in contrast, produced no such decrease. This may imply that the two drugs act at different levels in suppressing cell replication, and dithranol may be a useful tool for the further investigation of cyclic nucleotide metabolism.

A combined alkali extraction--ethidium bromide technique for the measurement of DNA in small pieces of tissue

Alkaline solutions (0.1--0.5 N NaOH) at elevated temperatures can be used to extract DNA from small pieces of tissue. RNA is destroyed by the treatment. In tissues which have been previously exposed to tritiated thymidine, aliquots from the extracting solution can be used directly for the determination of DNA by ethidium bromide fluorescence and radioactivity in both DNA and the nucleotide pool.

Studies on the plasma membrane of normal and psoriatic keratinocytes. 2. Cyclic AMP and its response to hormonal stimulation

Cyclic AMP levels have been determined for the first time in isolated keratinocytes. Values were more reproducible than those reported using epidermal slices. Evidence is presented to show that damage to hormone receptors is minimal. Other observations include the following: (1) Keratinocytes from psoriatic lesions showed reduced 'resting' levels of cyclic AMP as well as a diminished response to adrenaline. (2) Cyclic AMP levels were maximal in the basal cells, falling dramatically in fully differentiated keratinocytes. (3) The topical application of a corticosteroid (fluocinolone acetonide) did not modulate the response of adenyl cyclase to hormonal stimulation.

The effect of topical isoprenaline on psoriatic skin

Twelve patients with psoriasis were treated by the topical application of 0.1% isoprenaline sulphate ointment for 10 days. Topical white vaseline was used as a control in three patients with psoriasis. The mean glycogen level was found to be decreased significantly (from 120 +/- s.d. 40 to 58 +/- s.d. 26 mg/100 g of wet weight of involved skin) after topical application of 0.1 isoprenaline sulphate and the scaling also disappeared. Topical application of white vaseline did not produce any significant change in glycogen levels or scaling. The changes after isoprenaline application may have been due to an increase in the ratio of cyclic AMP/cyclic GMP which inhibited cell turnover and increased glycogenolysis.

Effects of topical prostaglandin E analogue on normal hairless mouse epidermal DNA synthesis

The in vivo topical effects of a synthetic analogue of prostaglandin E2 (15(S)-15-methyl PGE2 methyl ester [PGE2 analogue]), have been studied on the epidermis of hairless mice. One microgram of the PGE2 analogue increased DNA synthesis significantly by 5 hr, a maximum increase of 390% was reached by 12 hr, and DNA synthesis returned to control levels by 24 hr. Twenty micrograms of the PGE2 analogue reduced epidermal DNA synthesis for 12 hr after application, DNA synthesis was increased at 24 hr, returning to control levels by 48 hr. One hundred micrograms of topical PGE2 had no significant effect on epidermal DNA synthesis over 48 hr, but 1 mug of intradermal PGE2 increased DNA synthesis by 160% at 24 hr. These results suggest that topical 15(S)-15-methyl PGE2 methyl ester is biologically active compared with PGE2.

Periodic acid-Schiff (PAS) staining for glycogen in clinically normal psoriatic and non-psoriatic skin

PAS staining was used to assess the glycogen content of clinically normal forearm epidermis in 32 patients with active psoriasis, 30 patients with inactive psoriasis and 40 non-psoriatic subjects. Glycogen accumulation was greater in patients with active than in those with inactive psoriasis. The inactive psoriatics showed significantly less glycogen accumulation than the controls.

Multiple forms of cyclic nucleotide phosphodiesterase in pig epidermis

Pig epidermal cyclic nucleotide phosphodiesterases (EC 3.1.4.16) have been partially purified by DEAE-cellulose column chromatography. At least three different forms of the epidermal phosphodiesterases were identified. They were cyclic GMP-specific, cyclic GMP- and cyclic AMP-hydrolyzing and apparently a cyclic AMP-specific enzyme: the first two forms were soluble and the last was the particulate enzyme. The cyclic GMP-specific soluble fraction had a relatively low Km, the cyclic GMP- and cyclic AMP-hydrolyzing fraction had a high Km for the respective substrates and the third particulate enzyme had both high and low Km values for cyclic AMP. The cyclic GMP-hydrolyzing enzyme was localized almost entirely in the soluble fraction, whereas cyclic AMP-hydrolyzing enzyme was distributed to both soluble and particulate fractions. Thus, our studies show that the multiple forms of pig epidermal enzyme differ distinctly in their substrate affinity, specificity and subcellular distribution.