We hypothesized that muscle level of the cytokines would be higher in patients than controls, increase in response to a repetitive tooth-clenching task in a similar manner in both groups, and correlate to pain intensity, fatigue and level of stress and anxiety.
Finally, evidence that these responses reflect the development of senescence, we found that the increase in the muscle level of miR-29 at 30 days after electroporation of mmu-miR-29 and this accompanied by an increase in the level of the senescence marker, SA-β-gal.
Chronic myalgia is associated with higher muscle levels of certain algesic biomarkers.
Increased muscle levels of other inflammatory markers, such as serotonin and glutamate have also been reported in chronic localized myalgia [15, 23, 35].
This study showed that the muscle levels of IL-6, IL-7, IL-8 and IL-13 were increased in patients with TMD myalgia and increased further in response to experimental tooth-clenching, as did jaw-muscle pain and fatigue.
Also, muscle levels of TNF and IL-1β were increased in trapezius trigger points in patients with myofascial pain [21, 22], and IL-6 increased in the painful trapezius muscle of patients with whiplash-associated disorders (WAD) [23].
Another issue could be that we used topical anesthetics (EMLA cream) to anesthetize the skin before insertion of the microdialysis catheter, which possibly might influence the interstitial muscle levels of biomarkers.
This is the first study to show elevated muscle levels of the pro-inflammatory cytokines IL-6 and IL-8 and the anti-inflammatory cytokines IL-7 and IL-13 in painful jaw muscles of patients with TMD myalgia which supports the hypothesis that patients with TMD myalgia have higher levels of cytokines.
Although plasma cytokines were not analyzed in this study, muscle levels of IL-6 and IL-8 (but not IL-1β or TNF) were reported higher than plasma levels in patients with fibromyalgia, supporting that they are produced in the muscle [25].
Another study compared the effects in rats receiving during days 10 to 21 after Trichinella spiralis - induced infection either Lactobacillus paracasei Lactobacillus johnsonii Bifidobacterium longum, or Bifidobacterium lactis; Lb paracasei but not the other LAB attenuated muscle hyper-contractility, reduced the infection-associated Th- 2 response and muscle levels of TGF-β, COX-2 and PGE2 [55].
The increased muscle levels of IL-7 and IL-13 in the patients in this study imply that anti-inflammatory cytokines are locally produced to counteract this effect, although this may not be sufficient as LPS-stimulated monocytes from TMD-patients showed a blunted response of IL-10 [38].
