Turbo-PUVA: dihydroxyacetone-enhanced photochemotherapy for psoriasis: a pilot study

Dihydroxyacetone: A User Guide for a Challenging Bio-Based Synthon

1,3-dihydroxyacetone (DHA) is an underrated bio-based synthon, with a broad range of reactivities. It is produced for the revalorization of glycerol, a major side-product of the growing biodiesel industry. The overwhelming majority of DHA produced worldwide is intended for application as a self-tanning agent in cosmetic formulations. This review provides an overview of the discovery, physical and chemical properties of DHA, and of its industrial production routes from glycerol. Microbial fermentation is the only industrial-scaled route but advances in electrooxidation and aerobic oxidation are also reported. This review focuses on the plurality of reactivities of DHA to help chemists interested in bio-based building blocks see the potential of DHA for this application. The handling of DHA is delicate as it can undergo dimerization as well as isomerization reactions in aqueous solutions at room temperature. DHA can also be involved in further side-reactions, yielding original side-products, as well as compounds of interest. If this peculiar reactivity was harnessed, DHA could help address current sustainability challenges encountered in the synthesis of speciality polymers, ranging from biocompatible polymers to innovative polymers with cutting-edge properties and improved biodegradability.

An alternative approach for quantification of glyceraldehyde and dihydroxyacetone as trimethylsilyl derivatives by GC-FID

A method for quantification of glyceraldehyde (GA), dihydroxyacetone (DHA) and glycerol (GLY) by gas chromatography coupled to a flame ionization detector (GC-FID) involving one-step derivatization into trimethylsilyl ethers is presented. In pyridine, DHA and GA showed predominant peaks assigned to dimeric structures and smaller peaks corresponding to the monomers. The later were identified by GC-MS as their completely derivatized molecules and were useful for construction of calibration curves with high linear correlation. On the other hand, DHA dimers were completely dissociated in water but GA dimers remained whereas with both, intermediates peaks arose which were associated to hydrated trymethyil silyl species. A calibration approach involving the sum of areas of most relevant peaks associated to aqueous solutions of GA and DHA was developed. Replicates measurements of a problem solution were in accordance with the results obtained by a well stablished HPLC technique. The coefficient of variation was below 5% for GLY and below 12% for GA and DHA. Compared with the HPLC method, the new GC-FID method presented a similar limit of quantification in the case of GA whereas for GLY and DHA a one-order-of-magnitude increase of sensitivity was achieved. TMS derivatives of GA and DHA without prior oximation enable a useful technique to study the equilibrium of the different tautomeric forms in solution.

Synthetic Biomaterials from Metabolically Derived Synthons

The utility of metabolic synthons as the building blocks for new biomaterials is based on the early application and success of hydroxy acid based polyesters as degradable sutures and controlled drug delivery matrices. The sheer number of potential monomers derived from the metabolome (e.g., lactic acid, dihydroxyacetone, glycerol, fumarate) gives rise to almost limitless biomaterial structural possibilities, functionality, and performance characteristics, as well as opportunities for the synthesis of new polymers. This review describes recent advances in new chemistries, as well as the inventive use of traditional chemistries, toward the design and synthesis of new polymers. Specific polymeric biomaterials can be prepared for use in varied medical applications (e.g., drug delivery, tissue engineering, wound repair, etc.) through judicious selection of the monomer and backbone linkage.

Crosslinking of scleral collagen in the rabbit using glyceraldehyde

PURPOSE

To strengthen rabbit sclera in vivo using chemical crosslinking with glyceraldehyde for a scleral-based treatment of progressive myopia.

SETTING

Department of Ophthalmology, Martin-Luther-University, Halle, Germany.

METHODS

Five chinchilla rabbits were treated with sequential sub-Tenon injections of 0.15 mL 0.5 M glyceraldehyde into the superonasal quadrant of the right eye 5 times during 14 days. The rabbits were humanely killed and biomechanical stress-strain measurements of scleral strips from the treatment area were performed and compared with nontreated contralateral control sclera using a microcomputer-controlled biomaterial tester. The treated eyes were examined histologically by light microscopy to exclude possible adverse effects.

RESULTS

Following the crosslinking treatment, the ultimate stress was 15.8 MPa +/- 6.0 (SD) versus 3.1 +/- 0.3 MPa in the controls (increase of 409.7%; P<.02), the Young modulus was 129.6 +/- 53.7 MPa versus 11.5 +/- 1.8 MPa in the controls (increase of 1027%, P<.01), and ultimate strain was 19.8% +/- 2.6% MPA versus 38.2% +/- 5.1% MPA in the controls (decrease of 48.2% P<.05). Histologically, mild side effects were found in the peripheral cornea adjacent to the treatment area, with some inflammatory infiltrate and moderate loss of keratocytes.

CONCLUSIONS

Glyceraldehyde crosslinking of scleral collagen increased the scleral biomechanical rigidity efficiently. Glyceraldehyde can be easily applied by sequential parabulbar injections. There were no side effects on the retina, so the new method might become a treatment modality for strengthening scleral tissue to prevent progressive myopia.

The Maillard Reaction for Sunlight Protection

During seven months of a clinical trial in spring, summer, and fall, 30 UVA/B/Soret band-photosensitive patients used sequential topical applications of dihydroxyacetone (DHA) followed by naphthoquinone only at bedtime and received excellent photoprotection without a single therapeutic failure or loss of any patient to follow-up. Eighteen of the 30 patients extended the limits of their photoprotection repeatedly over a seven-month period to tolerate without sunburns six to eight hours of midday sunlight under all kinds of occupational and recreational environmental conditions. Previously, the use of 3% DHA topically in earlier studies gave only a sun protection factor (SPF) of 3. In this reanalysis of the original notes of a previous clinical study of the melanoidins produced by DHA followed by naphthoquinone in the keratin layers of the epidermis of minimally pigmented Caucasian photosensitive patients, it is determined that these patients received a minimal UVB photoprotection of SPF 18 or more. This represents at least a sixfold amplification of the UVB photoprotective effect over the use of only dihydroxyacetone in the Maillard reaction.

Using light in dermatology: an update on lasers, ultraviolet phototherapy, and photodynamic therapy

Indications for light-based treatments, such as lasers, UV phototherapy, and photodynamic therapy, are rapidly increasing within the arena of skin disorders. Physicians can remain current in their understanding of these modalities if they understand a few basic principles outlined in this article. Once these concepts are understood, all the rapid advances can be kept in perspective and physicians can apply the most appropriate technology to the care of their patients while informing them about the limitations of overmarketed but poorly proved strategies.

Factors influencing sunless tanning with dihydroxyacetone

BACKGROUND

Sunless tanning preparations have been used for more than 50 years and are still very popular because they provide temporary pigmentation resembling an ultraviolet-induced tan. The pigment is the product of reactions between dihydroxyacetone (DHA) and amino acids in the stratum corneum.

OBJECTIVES

To understand the factors that influence the reactions of DHA with amino acids in the stratum corneum with the ultimate goal of producing pigmentation with greater photoprotection.

METHODS

The influence of hydration and/or oxygen on the development of DHA-induced pigment was assessed in vivo using an occlusive dressing and ex vitro on human epidermal preparations. Two spectroscopic techniques, diffuse reflectance and fluorescence emission, were used to monitor the extent of pigment development. The optimal relative humidity for DHA-induced pigmentation was assessed on the epidermal preparations. The formation of products from reactions between DHA and nine amino acids was studied in solutions buffered at pH 5 and 7.

RESULTS

Development of DHA-induced pigmentation was inhibited by a 24-h occlusive dressing but appeared after its removal, indicating that DHA was still present. High hydration but not the absence of oxygen inhibited coloration of occluded skin. The extent of pigmentation did not vary in a simple manner with hydration, as pigment formation was positively correlated with humidity from 0 to 75% but negatively correlated from 75 to 100%. Lysine, glycine and histidine reacted most rapidly with DHA, with reaction rates greater at pH 7 than at pH 5. The products absorbed with maxima at wavelengths up to 340 nm.

CONCLUSIONS

These results indicate that extent of hydration, pH and availability of certain amino acids influence the development of DHA-induced pigmentation in the stratum corneum and suggest that manipulation of these factors might produce pigmentation with greater photoprotection.

Influence of hydration on dihydroxyacetone-induced pigmentation of stratum corneum

Dihydroxyacetone, the browning ingredient in sunless tanning formulations, reacts with amino acids in the outer stratum corneum to form a mixture of high molecular weight pigments. Our initial observations indicated that high hydration of dihydroxyacetone-treated skin completely inhibited development of pigmentation. To investigate the mechanism underlying this effect, studies were carried out in isolated murine epidermis, polyvinyl alcohol/lysine films, and lysine in glycerol/water solvent. Murine epidermis treated with dihydroxyacetone showed a biphasic dependence on relative humidity: maximum pigmentation developed at 84% relative humidity and minimum pigmentation at 0% and 100% relative humidity. Filaggrin proteolysis, which shows a similar dependence on relative humidity and provides free amino acids in the outer stratum corneum, did not account for the relative humidity dependence of dihydroxyacetone pigmentation. A similar biphasic pigmentation response was obtained when polyvinyl alcohol film containing lysine was treated with dihydroxyacetone and incubated at various relative humidities, indicating that the structure of the stratum corneum was not a major factor. To remove the influence of the matrix, the reaction of dihydroxyacetone with lysine was followed at varying concentrations of water in mixed glycerol/buffer solvent. Again, greater pigment formation was found at an intermediate level of water (6% vol/vol) and little pigmentation at 0% and 100% water content. These results are consistent with a requirement for water at low relative humidity, which facilitates formation of free amine groups needed for the initial reaction with dihydroxyacetone, and with inhibition of the dehydration reactions by water through the law of mass action at high relative humidity.

Skin pigmentation enhancers

The highest incidences of cancer are found in the skin, but endogenous pigmentation is associated with markedly reduced risk. Agents that enhance skin pigmentation have the potential to reduce both photodamage and skin cancer incidence. The purpose of this review is to evaluate agents that have the potential to increase skin pigmentation. These include topically applied substances that simulate natural pigmentation: dihydroxyacetone and melanins; and substances that stimulate the natural pigmentation process: psoralens with UVA (PUVA), dimethylsulfoxide (DMSO), L-tyrosine, L-Dopa, lysosomotropic agents, diacylglycerols, thymidine dinucleotides, DNA fragments, melanocyte stimulating hormone (MSH) analogs, 3-isobutyl-1-methylxanthine (IBMX), nitric oxide donors, and bicyclic monoterpene (BMT) diols. These agents are compared with regards to efficacy when administered to melanoma cells, normal human epidermal melanocytes, animal skin, and human skin. In addition, mechanisms of action are reviewed since these may reveal issues related to both efficacy and safety. Both dihydroxyacetone and topically applied melanins are presently available to the consumer, and both of these have been shown to provide some photoprotection. Of the pigmentation stimulators, only PUVA and MSH analogs have been tested extensively on humans, but there are concerns about the safety and side effects of both. At least some of the remaining pigmentation stimulators under development have the potential to safely induce a photoprotective tan.

In vivo formation of Maillard reaction free radicals in mouse skin

The Maillard browning reaction between carbohydrates and amines is part of an extensive series of reactions that is the basis for the brown color caused by the "sunless tanning" agent dihydroxyacetone in self-tanning products. The initial stages of the reaction are quite complex, but the ultimate products are brown polymers known collectively as melanoidins. We have now used electron spin resonance to show that radicals are produced in vivo by the Maillard reaction, initiated by treating the skin of hairless mice with a solution of dihydroxyacetone in buffer. Dihydroxyacetone was used as the carbohydrate because it is simple but highly reactive and is the only USFDA approved color additive for the production of a sunless tanning response on skin. Treated skin turned brown within 24 h and showed an electron spin resonance signal after sacrifice of the animal. The control sample, consisting of untreated skin from the same animal, remained its original pink color and had no electron spin resonance signal. In corresponding ex vivo experiments in which mouse skin was soaked in dihydroxyacetone solutions, it was conclusively demonstrated that the presence of the dihydroxyacetone was required for radical formation in skin. In both the in vivo and ex vivo reactions the electron spin resonance signal consists of a broad single line with a peak-to-peak linewidth of 15 Gauss and a g value of 2.0035. We suggest that dihydroxyacetone interacts on skin through a free radical mediated reaction similar to its in vitro reactions with amines and amino acids.

Tanning preparations

Increasing consumer awareness as to the hazards of UV light should fuel ongoing interest in self-tanning products. As a result of the benign toxicologic profile of DHA, products containing DHA represent a safe alternative to UV-induced tanning. The results obtained with these products depend on the final formulation, the individual application technique, and the consumer's complexion type. Greater experience in formulation combined with increasing sophistication on the part of the consumer should lead to continuing growth in interest and satisfaction with the use of DHA-containing sunless or self-tanning products. Individuals need to be informed that these products do not offer significant protection against UV-B. If formulated with standard sunscreens, consumers should be cautioned that the duration of UV protection is more short-lived than the color change.

Photodynamic therapy: a new concept in medical treatment

A new concept in the therapy of both neoplastic and non-neoplastic diseases is discussed in this article. Photodynamic therapy (PDT) involves light activation, in the presence of molecular oxygen, of certain dyes that are taken up by the target tissue. These dyes are termed photosensitizers. The mechanism of interaction of the photosensitizers and light is discussed, along with the effects produced in the target tissue. The present status of clinical PDT is discussed along with the newer photosensitizers being used and their clinical roles. Despite the promising results from earlier clinical trials of PDT, considerable additional work is needed to bring this new modality of treatment into modern clinical practice. Improvements in the area of light source delivery, light dosimetry and the computation of models of treatment are necessary to standardize treatments and ensure proper treatment delivery. Finally, quality assurance issues in the treatment process should be introduced.