Cutaneous alkaline phosphatase: a biochemical study

D-peptide hydrogels as a long-acting multipurpose drug delivery platform for combined contraception and HIV prevention

New multipurpose prevention technology products for use by women, focused on reducing HIV infection and preventing unwanted pregnancies, are a global health priority. Discreet long-acting formulations will empower women with greater choice around their sexual health. This paper outlines the development of a long-acting technology that enables multiple drugs to be incorporated within one injectable platform. This fixed-dose combination product is formed from a phosphorylated D-peptide (naphthalene-2-ly)-acetyl-diphenylalanine-lysine-tyrosine-glycine-OH (Napffky(p)G-OH) that enables the highly hydrophobic drugs MIV-150 (HIV antiretroviral) and etonogestrel (contraceptive) to be solubilized together within aqueous solvents. Upon subcutaneous injection, this D-peptide-drug combination self-assembles in response to phosphatase enzymes present within the skin space to form an in situ forming drug-releasing hydrogel depot. Oscillatory rheology confirmed the formation of hydrogels, which began within ∼10 s exposure to 3.98 U/mL phosphatase enzymes and continued for ∼198 mins for a Napffk(MIV-150)y(p)G-OH + Napffk(ENG)y(p)G-OH combination (8:2 ratio). Biostability against proteases, an important consideration for long-acting injectables, was demonstrated for at least 28 days in vitro. Covalent attachment of each drug to the D-peptide via an ester linkage enabled sustained release of the drug in an unmodified form via hydrolysis of the D-peptide-drug linker. This significantly reduced the initial drug burst. Low toxicity was also demonstrated in vitro via cell culture (MTS, LHS, Live/Dead®) and within in vivo studies (H&E staining). The fixed dose combination was able to deliver clinically relevant concentrations of each drug to Sprague-Dawley rats for at least 49 days, providing proof-of-concept for the use of hydrogel-forming D-peptides (Napffky(p)G-OH) as a long-acting injectable platform for the delivery of multiple hydrophobic drugs.

Biology, environmental and nutritional modulation of skin mucus alkaline phosphatase in fish: A review

Alkaline phosphatase (AP) is a major, recently recognized component of innate immunity. The intestinal AP (IAP) isoform plays a pivotal role in controlling gastrointestinal and systemic inflammation in terrestrial mammals. This is so essentially through detoxification (by dephosphorylation) of proinflammatory microbial components that can no longer be recognized by so-called toll-like receptors, thus preventing cellular inflammatory cascade activation. A unique feature of fish is the presence of AP in skin and epidermal mucus (skin mucus AP) but its actual functions and underlying mechanisms of action are presently unknown. Here, we gather and analyse knowledge available on skin mucus AP in order to provide a holistic view of this important protective enzyme. Our main conclusions are that skin mucus AP is responsive to biotic and abiotic factors, including nutrients and bioactive feed components, prebiotics and probiotics. Importantly, both skin mucus AP and IAP appear to correlate, thus raising the interesting possibility that skin mucus AP be used as a proxy for IAP in future nutritional studies. Blood serum AP also seems to correlate with skin mucus AP, though biological interpretation for such relationship is presently unknown. Finally, the precise isoform/s of AP present in skin should be identified and underlying molecular mechanisms of skin mucus AP actions deciphered.

Is there life in the horny layer? Dihydropyridine and ryanodine receptors in the skin of female and male chickens (Gallus domesticus)

Previous findings in pigeons and chickens show that Ca(2+) may be accumulated inside the cornified skin cells and that Ca(2+) microenvironments with a lower- or higher-than-blood concentration may exist in the skin. It has been suggested that the skin may function as a secretory pathway or a reservoir for Ca(2+) recycling. To test this hypothesis, we studied the dermis and epidermis of female and male chickens in vivo to find out whether cellular mechanisms exist for the accumulation, recycling or secretion of Ca(2+). For calcium influx and intracellular Ca(2+) release, respectively, the density of dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs) was examined, using high-affinity (-)-enantiomers of dihydropyridine and ryanodine labelled with fluorophores. To investigate Ca(2+) utilization in the skin, the systemic and local activity of the enzyme alkaline phosphatase (ALP) and the concentration of ionic Ca(2+) were measured in plasma and in cutaneous extracellular fluid, collected by suction blister technique. We found that both DHPRs and RyRs were present in all skin layers from dermis to horny layer. However, receptor densities were highest in the surface layers. With a basic calcium-rich diet, receptor densities were higher in males, particularly in the dermis and mid-epidermis. After a reduction in the nutritional Ca(2+) input, receptor densities in males decreased to the same level as in females, in which the receptor densities were not affected by the amount of Ca(2+) in the diet or that resulting from coming out of lay. The extracellular concentration of ionic Ca(2+) per se was not found to affect the density of DHPRs and RyRs in the skin. Spatially, RyRs seem to be located in the periphery of the sebokeratinocyte. ALP activity was shown to be lower in the extracellular fluid than in the plasma in both sexes. However, activity in both extracellular domains increased significantly in females that had come out of lay. This was probably connected with the increased osteoblast activity related to the reformation of structural bone. In conclusion, voltage-sensitive L-type Ca(2+) channels for ion influx and RyRs for Ca(2+) release are present in the cells of the skin of female and male chickens. Higher densities in the males receiving excessive Ca(2+) imply an increased capacity for Ca(2+) influx and intracellular processing. Even though the functional interactions between DHPRs and RyRs in the sebokeratinocytes could not be demonstrated, peripheral colocation and high receptor densities at the level of exocytosis of the lamellar bodies point to their role as part of a signalling pathway for secretion. The finding that DHPRs and RyRs are present in the horny layer implies that the function of the outermost skin might be more active than had been previously thought and that this function might be both secretory and sensory.

In vitro phenotypic alteration of human melanoma cells induced by differentiating agents: heterogeneous effects on cellular growth and morphology, enzymatic activity, and antigenic expression

Sodium butyrate (butyrate), 5-azacytidine (5Aza-C), dimethyl sulfoxide (DMSO), and dimethyl formamide (DMF) were applied to a human melanoma cell line for the purpose of inducing pigmentation and terminal differentiation. The results are summarized as follows: 1) butyrate, DMSO, and DMF had a strong cytostatic effect, arresting cells in the G1 phase of the cycle; 2) butyrate caused a morphological change to spindle shape whereas DMSO and DMF produced rounded cells, without affecting the levels of vimentin and intermediate filaments; 3) tyrosinase activity and melanization were stimulated by DMSO and DMF but not by butyrate; 4) butyrate induced several membrane-bound enzyme activities (alkaline phosphatase and gamma-glutamyl transpeptidase); 5) changes in the expression of antigens related to tyrosinase activity (2B7 and 5C12) only partly corresponded to the changes in enzyme activity; 6) expression of the melanosomal B8G3 antigen was decreased by butyrate, DMSO, and DMF; and 7) the action of DMF resembled that of DMSO whereas 5Aza-C had little effect. The results indicate that these differentiating agents activate different sets of genes, the melanogenic pathway being activated independently of gamma-glutamyltranspeptidase. The down regulation of B8G3 antigen by these agents may provide a common focus for understanding the essential action of differentiation inducers in melanoma cells.

Modulation of phospholipase A2 activity in extracts of lesion-free psoriatic epidermis by alkaline phosphatase and a protein phosphatase inhibitor

Phospholipase A2 activity is raised in non-lesional psoriatic epidermis compared with normal epidermis. It has been shown that the activity of this enzyme is controlled by an inhibitory protein the inhibitory effect of which is increased by dephosphorylation. Treatment of epidermal extracts with alkaline phosphatase reduced the phospholipase A2 activity, both in normal and in lesion-free psoriatic epidermis. Inclusion of pyrophosphate, a protein phosphatase inhibitor, in the homogenizing medium caused the activity of phospholipase A2 in epidermal extracts from normal and lesion-free epidermis to be raised to the same high level. These results are consistent with the hypothesis that the raised phospholipase A2 activity in psoriatic epidermis is due to hyperphosphorylation of an endogenous inhibitor as a result of defective control of a phosphorylation/dephosphorylation mechanism. The relevance of these findings to other work is discussed.

Modulation of placental alkaline phosphatase activity and cytokeratins in human HN-1 cells by butyrate, retinoic acid, catecholamines and histamine

The effects of butyrate and retinoic acid in combination with catecholamines or histamine on the HN-1 human head and neck squamous carcinoma cell line were investigated analysing cell proliferation, placental alkaline phosphatase (PLAP) activity, and relative cytokeratin content. Butyrate inhibited cell proliferation in agar, whereas retinoic acid induced a small inhibitory effect. Butyrate enhanced PLAP activity in a time related manner in contrast to retinoic acid, which had no significant effect. However, retinoic acid inhibited the efficacy of butyrate to induce PLAP activity. A synergistic enhancement of PLAP activity was demonstrated after treatment of butyrate pretreated cells with catecholamines or histamine. The beta-adrenergic antagonist propranolol partly inhibited the aforementioned enhancement of PLAP activity, whereas the alpha-adrenergic antagonist phentolamine further enhanced PLAP activity. Indirect labeling of keratins with a polyclonal antibody showed that cytokeratin content was enhanced by butyrate but not by retinoic acid. Further analysis of cytokeratin content using four monoclonal antibodies showed that labeling of cytokeratins (5 + 8) was increased by butyrate. PLAP activity could be modulated by a concerted action of either butyrate plus retinoic acid or butyrate plus catecholamines or histamine, indicating a possible role for PLAP in tumour cell proliferation.

Response of the clinically uninvolved skin of psoriatic patients to standardized injury

Test sites on healthy controls and on the clinically uninvolved skin of psoriatic patients were stripped with tape, and eight variables were quantified at intervals during the subsequent healing process. In the control groups, the stratum corneum regenerated at a constant rate and the underlying skin showed elevations of metabolic activity peaking around days 2-4. In the psoriatic groups, we observed that (I) the response of the keratinizing zone is identical to that of the controls, (2) the proliferative response is initially normal but remains elevated rather longer than usual, and (3) the dermal capillaries (indicated by alkaline phosphatase activity) show a gross hyper-reactivity which is already apparent after 1 day and which persists for more than a week. These findings support our previous conclusion that metabolic alteration of the dermal capillary precedes epidermal hyperplasia in the pathogenesis of the psoriatic lesion.

Metabolic changes at the margin of the spreading psoriatic lesion

Keratotome slices were cut across the margins of rapidly-spreading psoriatic plaques. Each slice was divided into eight sections and in each section we measured the percentage cells in S phase and the levels of glucose-6-phosphate dehydrogenase (both related to epidermal proliferation), acid phosphatase (associated with keratinization) and alkaline phosphatase (a marker for dermal capillaries). Disturbances in the epidermis extended only 2 to 4 mm into the 'uninvolved' skin, whereas the capillaries were metabolically abnormal for a distance of about 2 cm ahead of the advancing edge of the plaque. This implies that changes in the capillary may precede those in the epidermis during the spread of the psoriatic lesion.