ALKALOIDS IN COSMETICS 235 the amount of capsaicin in over-the-counter preparations, including cosmetics, is allowed at a concentration of 0.025% (10). Warm feeling is created as a result of the release of pro-infl ammatory peptides (substance P and CGRP), which dilate blood vessels and in- crease the heat exchange surface with the environment, which increases heat loss (29). Capsaicin in lip products may be used in the cosmetic industry in all types of lip glosses or lipsticks designed to enlarge lips. Increased blood fl ow through the blood vessels, caused by capsaicin, has the effect of enlarging the lips, which is manifested in the form of slightly swollen, toned, and red lips (30). However, this is a short-term result. Boudreau et al. (31) studied the effect of capsaicin on human sensory and vascular changes in 13 people. Applications of 1% capsaicin or vehicle cream to the glabrous lips and tongue were randomized between two two-trial sessions. The capsaicin trial followed the vehicle trial for each session. Before and after 5, 15, and 30 min capsaicin or vehicle cream application, blood fl ow and temperature were measured by laser-Doppler imaging and thermography. Increases in blood fl ow and temperature occurred after 5 min of capsaicin application. Van der Schueren et a l. (32) showed that 1,000 micrograms of capsaicin produced the maximum response between 30 and 45 min after application, and at 60 min time point, there was decrease in the blood fl ow. By using hai r and scalp care products (masks with capsaicin), there is increased microcir- culation of the scalp blood. Because of local irritation caused by capsaicin and increased blood fl ow, platelets are delivered to the scalp, including growth factors and cytokines. These compounds act immediately, leading to the activation of cell renewal, which affects skin regeneration as well as hair growth. The effect of capsaicin on hair growth was stud- ied by Lee et al. (33). After depilation of the back skin of mice, they divided mice into 4 groups, i.e., control, capsaicin, minoxidil, and co-applied group. They examined hair re- growth after depilation in terms of macroscopic examination, image analysis using pho- totrichogr ams, measurement of hair regrowth length, and microscopic examination. Hair growth of capsaicin group and minoxidil group began faster than that of co-applied group and control. Thereafter, hair growth of the capsaicin group was observed as the fastest, followed by the minoxidil group, co-applied group, and control. On microscopic exami- nation, capsaicin was able to make the hair cycle faster and shorter than control. These results suggest that capsaicin can not only induce the anagen phase quickly but also sus- tain constant effect on hair growth. Capsaicin sh ows the highest solubility in a lipophilic solvent (fat and oil) at pH = 8, but at pH = 5, the solubility of capsaicin is slightly lower. The pH of the skin is normally acidic, ranging in pH values of 4–6 (34) combining these two facts, it can be concluded that capsaicin may show a high affi nity for lipophilic cell membranes of the scalp, pene- trating deep into the tissues transdermally and so transcellularly (35). Another group of cosmetics with capsaicin are creams, slimming balms and products aimed at help in the fi ght against cellulite. Figure 2. Chemical structure of capsaicin (77).
JOURNAL OF COSMETIC SCIENCE 236 According to research conducted on Sprague–Dawley rats by Joo et al. (36), capsaicin prevents the transcription of protein genes that intensify the process of adipogenesis, in other words, accumulation of white adipose tissue. In this study, rats were divided into the normal control group, the high-fat group with capsaicin, and the high-fat group without capsaicin. This alkaloid was administered in dose 10 mg/kg BW by oral injec- tions. During the proteomic ana lysis of white adipose tissue, 37 proteins were detected and identifi ed wh ose expression was modulated in response to high-fat diet. Joo et al. (36) showed that under the infl uence of dietary capsaicin, the amount of mRNA of the key white adipose tissue transcription factors, PPARγ and C/EBPR, decreased signifi cantly. The weight difference at the beginning and at the end of the study for control group was 240 g, for the high-fat group without capsaicin was 313 g, and for high-fat group with capsaicin was 285 g (36). Capsaicin also contributes to the regulation of transcription of genes responsible for the production of enzymes that catalyze the hydrogenation of fats. In Lee et al. (37) studies conducted on the mouse 3T3-L1 cell line, fully differentiated adipocytes were treated with 0.1, 1, or 10 μmol/L capsaicin for 24 h. The intracellular lipid content was decreased in a dose-dependent manner in the presence of 0.1, 1, or 10 μmol/L capsaicin, by 3.2%, 6.9%, and 14%, respectively. The TG content of cells was also decreased by 15%, 21%, and 33%. Treatment with capsaicin resulted in a decrease in the intercellular lipid content and an increase in the amount of glycerol released into the medium, an indicator of the stimulation of lipolysis. Capsaicin is involved in the breakdown of fat in rodent adipocytes, and also increases the catabolism of intracellular fats (37). These processes are controlled by regulat- ing the expression of genes encoding proteins involved in catabolic lipid processes. Research on laboratory animals applies to humans therefore, it can be assumed that the mechanisms that occur in animals will be the same as in humans. Each of these processes leads to a de- crease in the amount of body fat, which can be a method of fi ghting cellulite. C apsaicin also has antioxidant properties that consist in reducing the intensity of lipid peroxidation processes. As an example, scientists cite delayed LDL lipoprotein oxidation (38). Serum lipid oxidation was examined by incubation of human serum with increasing concentrations (0.1, 0.5, 0.7, 1, 2, and 3 μM) of capsaicin, dihy drocapsaicin, and sub- jected to copper (100 μM)-induced oxidation. Copper-induced oxidation of serum was undertaken using the method described by Schnitzer et al. (39). At a concentration of 0.7 μM, the rate of oxidation was reduced by 42 and 45% for capsaicin and dihydro capsaicin, respectively (40). Delaying the lipid oxidation process can be of great importance when extending the shelf life of cosmetics containing a high fat content. Capsai cin has been shown to maintain the durability of various artifi cial materials, e.g., polyethylene—one of the most popular component cosmetic packaging. Capsaicin blocks the production of oxygen-free radicals and hydroxide anions, even in the presence of γ waves that activate their formation (41). The evident increase in the oxidation induction time (OIT) is the proof of the effi cient antioxidant effi ciency of capsaicin. The presence of capsaicin in low-density polyethylene (LDPE) brings about the delay in the OIT values by 1.6 times relative to neat polymer. The oxidation times of 150 and 260 min represent the values of 10 times longer for LDPE stabilized with capsaicin than for pure LDPE re- ceived irradiation dose of 30 kGy (41). Publishe d research shows that a plant extract with high capsaicin content has the effect of inhibiting the growth of some bacterial cultures. Both alcoholic and aqueous paprika
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