In vivo phosphorus spectroscopy of human skin

Skin phosphocreatine

BACKGROUND/PURPOSE

The skin has the unique ability to survive ischemia associated with skin grafts, flaps and hair transplantation procedures. Spectroscopic data later confirmed by chromatography, immunohistochemistry and molecular biology techniques identified the presence of large quantities of phosphocreatine in human skin. Phosphocreatine molecules regenerate ATP cellular reserves during ischemia. This reaction is mediated by creatine phosphokinase enzymes that were also isolated and studied in normal and diseased skin.

METHODS

Literature search revealed important contributions by US, Swiss, German, French, Scandinavian and Japanese investigators in the development and understanding of this research field.

RESULTS

Serum creatine phosphokinase levels are elevated in burn victims and patients with toxic epidermal necrolysis. Phosphocreatine concentration and creatine phosphokinase activity are elevated in psoriatic skin and in non-melanoma malignancies in comparison with normal skin. Furthermore, skin phosphocreatine and creatine phosphokinase enzymes are localized almost exclusively within the epidermis and in hair follicles. Finally, phosphocreatine and creatine phosphokinase enzymes help to protect skin from UV damage.

CONCLUSIONS

Clearly, this research area is only starting to be appreciated by the scientific community. Topical and systemic phosphocreatine administration appears to reverse photodamage and improve wound healing. Spectroscopic monitoring of phosphocreatine and related phosphometabolites can be potentially used to monitor disease activity and respond to therapy in psoriasis, leg ulcers, skin malignancies and other skin conditions.

Advances in MR imaging of the skin

MR imaging of the skin is challenging because of the small size of the structures to be visualized. By increasing the gradient amplitude and/or duration, skin layers can be visualized with a voxel size of the order of 20 microm, clearly the smallest obtained for in vivo images in a whole-body imager. Currently, the gradient strength of most commercial systems enables acquisition of such a small voxel size, and the main difficulty has thus become to achieve sufficient detection sensitivity. The signal-to-noise ratio (SNR) can be increased either by increasing the magnetic field strength or by minimizing noise with small coils; cooling copper coils or superconducting coils can enhance the SNR by a factor of 3 or more. MR imaging, because of the large number of parameters it is able to measure, can provide more than the microscopic architecture of the skin: physical parameters such as relaxation times, magnetization transfer or diffusion, and chemical parameters such as the water and fat contents or phosphorus metabolism. In spite of the amount of information they have provided to date, MR imaging and spectroscopy have had limited clinical applications, mainly because cutaneous pathologies are easily accessible to the naked eye and surgery. However, MR technologies indeed represent powerful research tools to study normal and diseased skin.

Age-dependent response of energy metabolism of human skin to UVA exposure: an in vivo study by 31P nuclear magnetic resonance spectroscopy

PURPOSE

The aim of our study was to evaluate the in vivo energy metabolism of human skin as a function of age, in conditions of rest and after a mild stress caused by a suberythemal UVA irradiation.

METHODS

The kinetics of UVA-induced modifications in high-energy phosphorylated metabolites of young and old skins were non-invasively monitored over a period of 24 h using 31P nuclear magnetic resonance spectroscopy. In vivo 31P spectra were obtained on the ventral aspect of the wrist, using a NMR Imaging Spectrometer equipped with a double-tuned surface coil. Concentrations of phosphocreatine, inorganic phospate, adenosine tri-phosphate, phosphomono and phosphodiesters were calculated from the spectra and results were expressed as relative concentrations. A total of 20 subjects were enrolled in this study (n = 10 for the age group below 25 years and n = 10 for the age group above 55 years). A second experiment was then performed on 10 old subjects (mean age 60) who were treated on one wrist, twice a day for one month prior to UVA irradiation, with a product that contained active ingredients to restore barrier function and modulate the inflammatory response, the other wrist being an untreated control.

RESULTS

Baseline levels of phosphorylated metabolites were similar in young and old skins. A suberythemal dose of UVA (6 J.cm-2) led to a significant decrease in the PCr/Pi ratio (index of energy status) and a significant increase in the PME/PDE ratio (index of cellular turnover rate of lipid-related metabolites) within 1 h. The observed variations were transient and the recovery was complete at T + 24 h post-UVA, although recovery was significantly slower in the older group. The disturbances were significantly reduced after treatment of the older skin with a formula that restored barrier function of the stratum corneum and modulated the inflammatory response.

CONCLUSION

(i) baseline levels of energy metabolites in skin do not seem to vary with age; (ii) low dose UVA irradiation induces a rapid response in the energy metabolism of the skin; (iii) the kinetics of the response and recovery after an aggression by UVA suggest that older skin has significantly less energy rebound after a stress situation than younger skin; (iv) the energy reserve in older skin can be protected efficiently against UVA-induced stress by restoring barrier function and modulating the inflammatory response.

Creatine kinase and creatine transporter in normal, wounded, and diseased skin

Skin comprises many cell types that are characterized by high biosynthetic activity and increased energy turnover. The creatine kinase system, consisting of creatine kinase isoenzymes and creatine transporter, is known to be important to support the high energy demands in such cells. We analyzed the presence and the localization of these proteins in murine and human skin under healthy and pathologic conditions, using immunoblotting and confocal immunohistochemistry with our recently developed specific antibodies. In murine skin, we found high amounts of brain-type cytosolic creatine kinase coexpressed with lower amounts of ubiquitous mitochondrial creatine kinase, both mainly localized in suprabasal layers of the epidermis, different cell types of hair follicles, sebaceous glands, and the subcutaneous panniculus carnosus muscle. With exception of sebaceous glands, these cells were also expressing creatine transporter. Muscle-type cytosolic creatine kinase and sarcomeric mitochondrial creatine kinase were restricted to panniculus carnosus. Immediately after wounding of murine skin, brain-type cytosolic creatine kinase and a creatine transporter-subspecies were transiently upregulated about 3-fold as seen in immunoblots, whereas the amount of ubiquitous mitochondrial creatine kinase increased during days 10-15 after wounding. Healthy and psoriatic human skin showed a similar coexpression pattern of brain-type cytosolic creatine kinase, ubiquitous mitochondrial creatine kinase, and creatine transporter in this pilot study, with creatine transporter species being upregulated in psoriasis.

Measurement of suberythema UVA radiation effects on skin by 31P magnetic resonance spectroscopy

31P magnetic resonance spectroscopy (MRS) scans were obtained from the same anatomical location in four healthy Caucasian individuals before and after 1/2 MED UVA radiation. Suberythema UVA radiation induced in skin production of phosphomonoesters, phosphodiesters, and also depleted phosphocreatine and adenosine triphosphate (ATP). This data seems to indicate that 31P MRS is a sensitive enough technique to detect UVA induced changes in skin phosphometabolites. Furthermore, this data also appears to indicate that suberythema UVA radiation and dexamethasone induce in skin nearly identical pharmacodynamic effect.

Spatial localization with modified Fourier series windows. Application to the transmural 13C-nuclear magnetic resonance analysis of the in vivo myocardium

RATIONALE AND OBJECTIVES

A modified Fourier Series Window (FSW) method is introduced that provides a simple, reasonably accurate, solution to spatial localization for layers in nuclear magnetic resonance (NMR) spectroscopy. This method was developed because signal originating from spins immediately adjacent to the coil plane can leak into standard FSW localized spectra obtained from more distal layers.

METHODS

The B1 profile of the surface coil and a priori sample knowledge were used to generate modified FSW coefficients that largely compensate for contamination from proximal layers. These modified coefficients were used to acquire spatially localized spectra from a three-layered phantom containing inorganic phosphate, phosphocreatine, and pyrophosphate. Spatially localized spectra also were obtained from the open-chest canine myocardium.

RESULTS

The modified Fourier Series Window approach was validated using a quality assurance phantom. This method was then applied to the transmural analysis of 13C-containing metabolites in the in vivo canine myocardium during 3-(13)C sodium pyruvate infusion (n = 10). In vivo NMR spectra were characterized by resonances corresponding to the C2, C3, and C4 carbons of glutamic acid and to endogenous triacyglycerides and surface lipids. A transmural trend in metabolites could be observed under these conditions. This trend, however, was likely to result from the interference of surface lipids in the epicardial layer.

CONCLUSIONS

The authors demonstrate that the modified Fourier Series Window method can be applied in situations where signal-to-noise considerations limit the applicability of more sophisticated spatial localization methods. In addition, the authors report a slight gradient in the endogenous triacylglyceride resonance, which is likely to originate from the presence of surface lipids.

31P NMR studies of human skin using a modified zig-zag surface coil

Results are presented from an in vivo study of human skin in which a zig-zag surface coil together with a three-pulse Fourier Series Window (FSW) protocol have been used to obtain minimally contaminated 31P skin spectra of the posterior calf. Phantom experiments indicate that while the fall-off in the B1 field profile of the zig-zag surface coil is superior to conventional surface coil designs, it is still not sufficient on its own to reduce muscle signal contamination to acceptable levels in human studies. The additional spatial localization required is provided by the FSW, which reduces signal contamination to less than 30% of the total signal collected. In a study of 18 normal controls the measured pH was found to be relatively high (7.39 +/- 0.08), while the ratios of skin PCr/ beta-ATP (1.04 +/- 0.35) and PCr/Pi (1.67 +/- 0.4) were found to be low compared with that of skeletal muscle. In addition, substantial signal from phosphomonoesters and phosphodiesters were also observed.

Use of the Fourier series window protocol with a zig-zag surface coil in 31P NMR human skin spectroscopy. A theoretical study

The use of a zig-zag surface coil with a three-pulse Fourier Series Window (FSW) has been suggested as a means by which in vivo NMR spectroscopic studies of human skin can be performed. Using direct numerical simulations of the magnetic field profile of a 10 limb zig-zag surface coil, the role of the FSW in reducing NMR signals originating from the deeper skeletal muscle layers is examined theoretically. The extent of muscle signal contamination is determined for different coil inter-limb spacings and pulse width settings. The optimum inter-limb spacing for studying living human skin, that which minimizes signal contamination and maximizes skin signal collected, is shown to be between 4 and 6 mm. These calculations demonstrate that the FSW and zig-zag surface coil offer a protocol for investigating the metabolism of large areas of surface tissue while keeping signal contamination from the deeper skeletal muscle layers down to an acceptable level.