Topical Treatment of Skin Injury Inflicted in Mice by X-Ray Irradiation

BACKGROUND/AIMS

There is no treatment, without side effects, efficiently preventing or curing skin burns, caused by radiotherapy. A new experimental topical treatment protocol was assessed in mice receiving orthovoltage X-rays at an equivalent dose to that applied to human breast cancer patients in conventional radiotherapy.

METHODS

SKH-HR2 female hairless mice were irradiated on their dorsum with a total dose of 4,300 cGy during a 1-month period (20 fractions). The treatment group received a combination of 3 topical products, an oil-in-water cream, a gel containing Pinus halepensis bark aqueous extract, and an ointment containing olive oil extract of the marine isopod Ceratothoa oestroides. The positive control group was treated with a conventionally used commercial gel, whereas the negative control group did not receive any topical treatment. Skin alterations were evaluated by macroscopic examinations, measurements of transepidermal water loss (TEWL), melanin content, erythema intensity, hydration, and histopathology assessment.

RESULTS

Sixty days after radiation, TEWL and hydration values were abnormal and elements of acute, chronic, and granulomatous inflammation were present in all cases. The severest damage was detected in the deeper dermis. Treatment showed a comparatively beneficial effect on chronic and granulomatous inflammation while positive control was beneficial on acute inflammation.

CONCLUSION

Skin anti-inflammatory treatment was the most effective but must be applied for several months. Further preclinical studies should be conducted, assimilating a human cancer radiation therapeutic schema with the aim of optimizing skin inflammation treatment.

Modulation of repopulation processes in oral mucosa: experimental results

PURPOSE

Repopulation processes, i.e. the tissue regeneration responses to radiotherapy with increasing overall treatment time, are the predominant factors defining the radiation tolerance of turnover tissues, such as squamous epithelia of the skin or gastrointestinal tract. The purpose was to assess experimental approaches for the modulation, i.e. stimulation of repopulation, in normal oral mucosa.

MATERIALS AND METHODS

Numerous studies have been performed to identify and quantify the efficacy of repopulation processes in oral mucosa in experimental animal models, mainly mouse lip and tongue mucosa, and in some clinical studies. However, only a few investigations focused on the stimulation of these processes, aiming at a reduction in oral mucosal side-effects of radiotherapy. The present review summarizes the biological mechanisms underlying effective repopulation, and delineates experimental approaches for effective stimulation of these processes, eventually resulting in an increase in oral mucosal radiation tolerance.

RESULTS

Repopulation in oral mucosa is a complex process dominated by a substantial reorganization of the proliferative structure, including a loss of the stem cell division asymmetry and acceleration of stem cell proliferation, as well as abortive divisions of 'sterilized' cells. Repopulation in mouse oral mucosa is more effective if the initial dose intensity (weekly dose) during the first treatment week(s) is increased. Stem cell production occurs mainly during the treatment weeks, while during treatment breaks, including weekends, differentiating (transit) cells are preferentially produced. Stimulation of superficial cell loss, e.g. by topical administration of mild astringent agents, stimulates mucosal proliferation. This translates into increased radiation tolerance to fractionated irradiation in experimental systems, like mouse tongue mucosa. In clinical studies, a reduction of oral mucosal reactions using the same approach was found during an accelerated radiotherapy regimen, but not during conventionally fractionated protocols. Keratinocyte growth factor has been demonstrated to reduce oral mucosal reactions significantly to single dose and fractionated irradiation. This effect is presumably based on an interaction with repopulation processes.

CONCLUSIONS

Repopulation in oral mucosa is a highly complex process, which includes a substantial reorganization of the proliferative structure. In experimental models, its efficacy can be modulated by changes in the fractionation protocol, but more effectively by intervention in the regulation processes, e.g. by stimulation of proliferation through enhancement of cell loss. An alternative promising approach is the administration of growth factors, like keratinocyte growth factor, for effective modulation of oral mucosal repopulation. However, selectivity for the normal tissue, as well as biological mechanisms, must be studied in detail in relevant animal models.

Repair of skin damage during fractionated irradiation with gamma rays and low-LET carbon ions

In clinical use of carbon-ion beams, a deep-seated tumor is irradiated with a Spread-Out Bragg peak (SOBP) with a high-LET feature, whereas surface skin is irradiated with an entrance plateau, the LET of which is lower than that of the peak. The repair kinetics of murine skin damage caused by an entrance plateau of carbon ions was compared with that caused by photons using a scheme of daily fractionated doses followed by a top-up dose. Right hind legs received local irradiations with either 20 keV/microm carbon ions or gamma rays. The skin reaction of the irradiated legs was scored every other day up to Day 35 using a scoring scale that consisted of 10 steps, ranging from 0.5 to 5.0. An isoeffect dose to produce a skin reaction score of 3.0 was used to obtain a total dose and a top-up dose for each fractionation. Dependence on a preceding dose and on the time interval of a top-up dose was examined using gamma rays. For fractionated gamma rays, the total dose linearly increased while the top-up dose linearly decreased with an increase in the number of fractions. The magnitude of damage repair depended on the size of dose per fraction, and was larger for 5.2 Gy than 12.5 Gy. The total dose of carbon ions with 5.2 Gy per fraction did not change till 2 fractions, but abruptly increased at the 3rd fraction. Factors such as rapid repopulation, induced repair and cell cycle synchronization are possible explanations for the abrupt increase. As an abrupt increase/decrease of normal tissue damage could be caused by changing the number of fractions in carbon-ion radiotherapy, we conclude that, unlike photon therapy, skin damage should be carefully studied when the number of fractions is changed in new clinical trials.

Evidence for humoral effects on the radiation response of rat foot skin

The influence of perturbation of the physiologic state of the whole body on the outcome of radiation exposure has been examined in a rat foot model. Irradiation was carried out using 60Co gamma-rays. Moist desquamation was used as an endpoint. Rats were given a priming dose of 2 Gy, 4 Gy or 7 Gy to their whole body except their hind feet (partial body priming dose). After a variable time period both hind feet of these animals were irradiated with graded doses of 60Co gamma-rays. The incidence of moist desquamation in the irradiated feet of these animals was compared with the incidence of moist desquamation in animals that had not received the initial partial body priming dose. It was noticed that the incidence of moist desquamation in the rat foot skin of animals that received 7 Gy partial body priming dose 4 h prior to irradiation of their hind feet was significantly less than moist desquamation in control animals. The ED(50) value of 22.53+/-0.16 Gy for moist desquamation of the foot skin of control animals was significantly lower (p<0.01) than the value of 25.25+/-0.29 Gy obtained for animals that received a partial body priming dose of 7 Gy 4 h prior to irradiation of their hind feet. It was concluded that the response of rat foot skin to radiation was not purely the result of epidermal stem cell kill and that it can be modified by alterations in the overall physiological state of the animal's body brought about by a priming dose to the whole of the animal's body except the hind feet.

Modulation of accelerated repopulation in mouse skin during daily irradiation

BACKGROUND AND PURPOSE

The timing of acceleration of repopulation in the epidermis during daily irradiation is related to the development of skin erythema and epidermal hypoplasia. Therefore, the relationship between impairment of the epidermal barrier function, the dermal inflammatory response and epidermal hypoplasia with the acceleration of repopulation was investigated. MATERIALS AND PURPOSE: Skin fields of approximately 1 cm2 on the thighs of TUC mice were given five daily fractions of 3 Gy in each week followed by top-up doses at the end of the first, the second, or the third week to determine residual epidermal tolerance and to calculate repopulation rates in weeks 1, 2, or 3. Systemic modulation of repopulation was attempted by daily indomethacine during fractionated irradiation whereas tape stripping or UV-B exposure before the start of fractionated irradiation attempted local modulation. In parallel experiments, the water permeability coefficient of the epidermis was determined ex vivo by studying transepidermal transport of tritiated water.

RESULTS

Without modulation, no repopulation was found in the first week of daily fractionation but repopulation compensated 30% of the dose given in week two and 70% of the dose given in week three. Only tape stripping before the start of fractionated irradiation accelerated repopulation in week one. UV-B had no effect on repopulation although it stimulated proliferation as much as tape stripping. Indomethacin did not suppress acceleration of repopulation. A significant increase in transepidermal water loss was found but only after repopulation had already accelerated.

CONCLUSIONS

Acceleration of repopulation in mouse epidermis during daily-fractionated irradiation is not related to the simultaneous development of an inflammatory response. Also, the loss of the epidermal barrier function is not involved in the development of the acceleration response, which rather seems to be triggered directly by the decreased cellularity of the epidermis.

Nuclear and non-nuclear targets of genotoxic agents in the induction of gene expression. Shared principles in yeast, rodents, man and plants

The interplay between environmental cues and the genetic response is decisive for the development, health and well-being of an organism. For some environmental factors a narrow margin separates beneficial and toxic impacts. With the increasing exposure to UV-B this dichotomy has reached public attention. This review will be concerned with the mechanisms that mediate a cellular genetic response to noxious agents. The toxic stimuli find access to the regulatory network inside cells by interacting at several points with cellular molecules - a process that converts the 'outside information' into 'cellular language'. As a consequence of such interactions, many adverse agents cause massive signal transduction and changes of gene expression. There is an interesting conservation of the mechanisms from yeast to man. An understanding of the genetic programs and of their phenotypic consequences is lagging behind.