Treatments for obesity have been shown to reduce pain secondary to weight loss. Intestinal microbiota, as an endogenous factor, influences obesity and pain sensitivity but the effect of oral probiotic supplementation on musculoskeletal pain perception has not been studied systematically. The present study examined the effect of a single daily oral dose (1 × 109 CFU) of probiotics (
Physiological pain plays a life-essential protective role, while acute or chronic pathological pain indicates a medical problem that needs treatment and imposes a medical challenge [
Pain perception is a complex process including neuronal, nonneuronal, and cognitive processes modulated by peripheral and central factors. Neurotransmitters, immune cells, and hormones have been demonstrated to contribute in pathogenesis of chronic pain [
Since pain is a subjective concept and pain measurement is challenging, it is usually measured under controlled conditions, by responses to experimental stimuli as applied by mechanical, thermal, electrical, and chemical stimuli [
Pressure pain threshold (PPT) has been identified as a reliable and easy biomarker in multiple clinical pain states [
Pain threshold is influenced by several factors, including obesity, which alters adipose tissue metabolic and endocrine functions leading to alterations in systemic physiology including an increased release of fatty acids, hormones, and proinflammatory molecules that contribute to obesity associated complications [
Previous studies have demonstrated a relationship between intestinal microbiota and diseases including pain disorders [
The possible beneficial role of probiotic supplementation on management of chronic musculoskeletal pain is in its infancy and requires further investigation. To study the confounding factors under well-controlled conditions, experimental models in animals and humans are superior to patient studies. In particular, rodent behavioral models have been important tools for advancing our understanding of the physiology underlying nociception and pain [
In this study we seek to address if probiotic supplements can potentially overcome the deleterious effects of obesity and reduce pain sensitivity by assessing the effect of
Animal experiments in this study were carried out in accordance with the Guidelines for Animal Experimentation and Approval of “The Danish Animal Experiments Inspectorate” number 2014-15-0201-00026.
Twenty-four, 6-week-old male C57BL/6NTac mice were acquired (Taconic, Denmark) and housed in a room at 22°C to 24°C, with 60% relative humidity and 12 h dark-light cycles (light on from 0800 to 2000 h). Mice were allowed two weeks of adaptation and free access to their respective diets and tap water ad libitum during the study period.
Aliquots providing 1 × 109 CFU per mouse were prepared (based on manufactures guidelines) and stored at −20°C until administration. Shortly before use, the prepared probiotic aliquots were diluted in normal saline (0.25 mL per mouse) at room temperature as vehicle and administered orally to the NDPR and FDPR groups.
The ND and FD groups received oral administration of normal saline without probiotics. This process was repeated once every day during phase II (second 4 weeks) of the study. Probiotic administration was performed using a gavage needle to ascertain the presence of the probiotics in the gastrointestinal tract.
Sensitivity to mechanical stimulation, as a translational biomarker of pain sensitivity, was assessed by the electronic Von Frey (Bioseb, France). This test evaluates how soon a withdrawal of the paw will occur due to a standard mechanical pressure (pressure pain threshold, PPT, in grams). The more sensitive it is to pain, the faster the withdrawal reaction would be detected. The mice were weighed using a digital scale and the Von Frey test was performed once every two weeks 3 times on all mice. Mice were placed in an acrylic box restrainer (15 × 15 cm) with a metal mesh floor (5 × 5 mm square openings) to prevent extra movement while having enough space to show reaction to mechanical stimulation. A filament (0.1–10
At baseline and the end of weeks 4 and 8, blood samples were collected from the facial vein of conscious mice [
Data are shown as means ± standard deviation (SD). Repeated measures ANOVA was used to compare differences in pain sensitivity and weight between groups and over time points. Bonferroni
As expected, all groups demonstrated a rising trend throughout the study period. However, the FD group, which were on a high fat diet, gained more weight compared to the ND and resulting in a significant weight difference (
After week 4, both ND and FD groups maintained a rising trend in the weight, whereas the groups which received the probiotic supplement maintained a stable weight with no significant change up to week 8 (Figure
The abilities of
The stable weight of the FDPR and the rising trend in the FD group led to a nonsignificant difference at week 6 (
The NDPR group maintained a stable weight after the start of probiotic supplementation at week 4 whereas the ND group remained stable until week 8 (Figure
The results demonstrate striking changes in the pain pressure threshold (PPT) values in both NW and DIO mice after 4 weeks of the probiotic supplementation (Figure
At the start of the study (baseline) PPT ranged between 15 and 17.7 g. A slight increase in the PPT was observed during the first 2 weeks of the study with each group being maintained on their corresponding diet (normal or fat diet) with no significant difference (Figure
However, a clear significant (
The FD group continued the decreasing trend in (PPT) until week 8, whereas the FDPR group demonstrated an increasing PPT (lower pain sensitivity) after the start of probiotic supplementation (from week 4 to week 8) reaching a significant (
The ND group demonstrated a rise in the PPT between weeks 4 and 6 changing to a decreasing trend from weeks 6 to 8 (Figure
The NDPR group also demonstrated an increasing PPT (lower pain sensitivity) after the start of probiotic supplementation (from week 4 to week 8) reaching a significant (
At the end of this study, week 8, the results of PPT were significantly (
The serum lipid profiles (serum total cholesterol, LDL-cholesterol, and HDL-cholesterol) of the mice at the start of the study (base) and after 4 and 8 weeks of the respective diet with or without probiotic supplement are presented in Table
Lipid profiles in mice fed normal diet (ND), high fat diet (FD), normal diet with probiotics (NDPR), and fat diet with probiotics (FDPR) at the start of the study (base) and at 4 and 8 weeks into the study (4 W and 8 W). Provided values are the mean ± standard deviation. Similar superscripted letters demonstrate pairwise significant (
Lipid profile parameters | Base | ND 4 W | ND 8 W | NDPR 8 W | FD 4 W | FD 8 W | FDPR 8 W |
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LDL/VLDL |
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Total cholesterol |
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The novelty and main purpose of this study were to investigate the potential of the probiotic
Our results demonstrated that DIO group had a higher body weigh compared with NW. Both of the normal and fat diet groups receiving probiotic supplements maintained a stable weight whereas their corresponding diet group without probiotic supplementation continued to gain weight until the end of study at week 8. This observation supported the report by Sanchez et al. that the probiotics (L.
The gut’s microbial community is recognized as one of the particular factors related to obesity and metabolic disorders [
Our study demonstrated that total cholesterol levels and LDL/VLDL levels had a rising trend over time in both normal and fat diet groups. Both of the NW and DIO groups receiving probiotic supplements demonstrated lower total cholesterol and LDL/VLDL levels while their corresponding diet group without probiotic supplements showed higher total cholesterol and LDL/VLDL levels throughout the study. Obesity is generally accompanied by an increased concentration of serum total cholesterol [
Many studies have reported the hypolipidemic effect of several probiotics strains in animals which is also observed and in line with the results of this study [
Several studies in humans also confirm the cholesterol-lowering effects of probiotics [
Our results demonstrated that DIO group had a lower mechanical pain pressure threshold (higher pain sensitivity) compared with groups treated with the normal diet.
Results from this study are in line with the findings of several previous reports generally demonstrating a significantly higher pain sensitivity in obese humans [
Obese rats receiving intradermal carrageenan injection in the paw were also shown to exhibit greater peripheral inflammation and hyperalgesia compared to lean rats [
It has been reported that obesity share a low grade chronic inflammatory state [
Guilherme et al. have reported that hypertrophy of adipocytes due to increased triglycerides uptake to these cells could result in the induction of a chronic inflammatory state by the recruitment of macrophages within the adipose tissue [
de Goeij et al. provide additional evidence that systemic inflammation accompanied by changes in pain perception could result in “inflammation-induced increased pain sensitivity”[
Other studies evaluating experimentally induced pain in obese and lean human and animal models in laboratory settings have resulted in somewhat controversial results. Some studies reported increased pain response to thermal noxious stimuli and pressure in obese rats [
Earlier studies have demonstrated that obese people exhibited decreased pain threshold to mechanical stimuli [
In this study a major increase in pressure pain threshold rates (lower sensitivity) was observed in groups with probiotic consumption compared with the groups with no probiotic supplement. Several lines of research have declared that probiotics exhibit powerful anti-inflammatory properties [
Regardless of the underlying mechanism, probiotics can be suggested as candidates of a novel strategy for weight and pain control in accordance with the management of pain in cases of obesity or normal weight. Translation of this result in humans can potentially suggest a novel therapeutic strategy in pain management of obese or normal weight individuals.
In conclusion this study demonstrated the potential of
The authors declare that there is no conflict of interests.
The authors would like to thank the Department of Health Science and Technology (Aalborg University, Denmark) for their research grant, Bifodan A/S for providing the probiotic supplements, the staff at the animal facility of Aalborg University Hospital, and Dr. Afshin Samani for his excellent guidance in statistical analysis.