Probiotic bacteria induce a 'glow of health'

Abstract

Radiant skin and hair are universally recognized as indications of good health. However, this 'glow of health' display remains poorly understood. We found that feeding of probiotic bacteria to aged mice induced integumentary changes mimicking peak health and reproductive fitness characteristic of much younger animals. Eating probiotic yogurt triggered epithelial follicular anagen-phase shift with sebocytogenesis resulting in thick lustrous fur due to a bacteria-triggered interleukin-10-dependent mechanism. Aged male animals eating probiotics exhibited increased subcuticular folliculogenesis, when compared with matched controls, yielding luxuriant fur only in probiotic-fed subjects. Female animals displayed probiotic-induced hyperacidity coinciding with shinier hair, a feature that also aligns with fertility in human females. Together these data provide insights into mammalian evolution and novel strategies for integumentary health.

Figure 1. Dietary supplementation with probiotic organisms induces lustrous fur in aged mice.

(A) Aged female C57BL/6 strain mice consuming probiotics exhibited significantly (p<0.0001) increased shininess quantifiable by sensory evaluation of human panelists blinded to mouse identity and using a standardized fur luster scale. (B) Reflectometry instrumentation using one degree (p<0.01) and five degree (p<0.01) field analyses revealed significantly (p<0.05) increased light reflectivity of mouse fur after eating probiotics, when tested under highly controlled lighting conditions. (C) Evaluation of mucocutaneous pH shows eating probiotic yogurt or purified probiotic bacteria induced more acidic conditions in skin, oral cavity, vaginal mucosa, and rectum of female mice. Similar trends in male animals did not reach statistical significance. (D) C57BL/6 mice consuming purified L. reuteri bacteria in drinking water had more rapid fur re-growth after shaving (right) when compared with matched mice drinking regular water (left).

Figure 2. Dietary supplementation with probiotics affects skin histology of mice.

(A) Probiotic-fed C57BL/6 male mice differ from their control diet-fed counterparts by having subcutaneous hair follicle profiles and a thicker skin. Hematoxylin and Eosin. Bars = 250 µm. Histomorphometrical analysis reveals significant (P<0.0001) probiotic diet-associated increase in (B) skin thickness and (C) subcutaneous hair follicles in both genders. The y-axis depicts the mean±SEM of histomorphometric counts in each experimental group.

Figure 3. Dietary probiotics increase anagen hair follicles and proliferation of sebocytes in aged mice.

(A) Quiescent (telogen-phase) hair follicles predominate in control-diet fed C57BL/6 mice. In contrast, the majority of the hair follicles are active (anagen-phase) in probiotic-fed mice of the same age. Active hair follicles undergoing rapid growth exhibit numerous proliferating cells (ki-67+). More rarely the regressing stage (catagen) contain caspase-3+ apoptotic cells. Control Telogen and Probiotic Anagen: Hematoxylin and Eosin. Probiotic Anagen-ki-67 and Probiotic Catagen-caspase-3: DAB chromogen, Hematoxylin counterstain. Bars = 50 µm. Classification of fifty intact longitudinally-sectioned hair follicles per treatment group were evaluated according to their stage of cycling (in B and C below). The distribution pattern of hair-follicle staging differs significantly (P<0.0001) among probiotic- and control diet-fed (B) male and (C) female mice. Numbers on the y-axis of bar graphs represent the mean±SEM of hair-follicles classified in each hair cycle stage. The % percentage of hair follicles in telogen (T), anagen (A) or catagen (C) stage is illustrated in circular graphs. Probiotic-fed mice of both genders show an anagen stage predominance. (D) Dietary supplementation with probiotics lead to a significant (P<0.0001) increase of sebocytes in skin pilosebaceous units. The y-axis stands for the mean±SEM of sebocyte counts per X20 high power field image. (E) The quantitative assessment of cellular proliferation in sebaceous glands with ki-67-specific immunohistochemistry (circular image) reveals that dietary probiotics increase the proliferative capacity of sebocytes. Numbers on the y axis of bar graphs correspond to the mean±SEM of the index of proliferating sebocytes per total number of sebocytes in x40 high power fields. Circular image: DAB chromogen, Hematoxylin counterstain. Bar = 25 µm.

Figure 4. Vaginal pH correlates with Lactobacillus abundance and peak fertility in humans.

(A) Bars show mean (+SEM) of vaginal pH for women as a function of number of years before or after peak fertility, which was taken to be 25 years of age for all subjects. (B) Vaginal pH is significantly associated with Lactobacillus abundance (Kendall’s Tau test; τ = −0.38; P = 3.2×10⁻⁸). Statistical differences between groups were assessed using the Mann-Whitney U test.

Figure 5. Dietary supplementation with purified Lactobacillus reuteri in drinking water mimics effects of eating probiotic yogurt on skin histology of aged mice.

Wild type C57BL/6 mice fed purified L. reuteri in drinking water differ significantly from their regular water-fed counterparts by having thicker skin and an increased subcutaneous hair follicle and sebocyte profile. (A) Histomorphometrical analysis reveals significant (P<0.0001) probiotic diet-associated increase in skin thickness and (B) number of subcutaneous hair follicles (P<0.05) in both genders. The y-axis depicts the mean±SEM of histomorphometric counts in each experimental group. (C) In mice treated with L. reuteri in drinking water, the majority of the hair follicles are active (anagen-phase). In contrast, control mice of the same age have predominantly quiescent (telogen-phase) hair follicles. The distribution pattern of hair-follicle staging differs significantly (P<0.0001) among L. reuteri- and control diet-fed in both male and female mice. Numbers on the y-axis of bar graphs represent the mean±SEM of hair follicles classified in each hair cycle stage. (D) Further, adding purified L. reuteri in drinking water lead to a significant (P<0.0001) increase of sebocytes in skin pilosebaceous units. The y-axis stands for the mean±SEM of sebocyte counts per X20 high power field image. Numbers on the y-axis of bar graphs correspond to the mean±SEM of the index of proliferating sebocytes per total number of sebocytes in x40 high power fields.

Figure 6. Lactobacillus reuteri –induced benefits in hair quality require anti-inflammatory cytokine Interleukin-10.

In contrast to wild type animals, feeding of L reuteri to aged C57BL/6 mice lacking interleukin (Il)-10 failed to improve subcutaneous hair follicle or sebocyte profile. (A) Histomorphometrical analysis in Il-10-deficient mice reveals insignificant differences in hair follicle activity and distribution (anagen-phase versus telogen-phase). Numbers on the y-axis of bar graphs represent the mean±SEM of hair-follicles classified in each hair cycle stage. (B) Likewise, sebocyte counts were not significantly different among L. reuteri- and control water-fed Il-10-deficient mice. Numbers on the y-axis of bar graphs represent the mean±SEM of sebocyte counts per X20 high power field image. (C) Evaluation of mucocutaneous pH shows eating probiotics induces more alkaline conditions in skin, oral cavity, rectum and vaginal mucosa of Il-10-deficient mice, contrasted with the more acidic conditions in WT female mice (Fig. 1D). (D) Depletion of Il-17A using anti-cytokine antibodies recapitulates the probiotic-induced glow of health features in the skin including hair follicle anagen phase predominance and vastly increased numbers of sebocytes in sebaceous glands. Numbers on the y-axis of bar graphs represent the mean±SEM of hair-follicles classified in each hair cycle stage. Numbers on the y-axis of bar graphs represent the mean±SEM of sebocyte counts per X20 high power field image.