*Article* **The Protective E**ff**ect of Brazilian Propolis againstGlycation Stress in Mouse Skeletal Muscle**

#### **Tatsuro Egawa 1,2,\*, Yoshitaka Ohno 3, Shingo Yokoyama 3, Takumi Yokokawa 1, Satoshi Tsuda 1, Katsumasa Goto 3,4 and Tatsuya Hayashi 1**


Received: 20 August 2019; Accepted: 24 September 2019; Published: 25 September 2019

**Abstract:** We investigated the protective effect of Brazilian propolis, a natural resinous substance produced by honeybees, against glycation stress in mouse skeletal muscles. Mice were divided into four groups: (1) Normal diet + drinking water, (2) Brazilian propolis (0.1%)-containing diet + drinking water, (3) normal diet + methylglyoxal (MGO) (0.1%)-containing drinking water, and (4) Brazilian propolis (0.1%)-containing diet + MGO (0.1%)-containing drinking water. MGO treatment for 20 weeks reduced the weight of the extensor digitorum longus (EDL) muscle and tended to be in the soleus muscle. Ingestion of Brazilian propolis showed no effect on this change in EDL muscles but tended to increase the weight of the soleus muscles regardless of MGO treatment. In EDL muscles, Brazilian propolis ingestion suppressed the accumulation of MGO-derived advanced glycation end products (AGEs) in MGO-treated mice. The activity of glyoxalase 1 was not affected by MGO, but was enhanced by Brazilian propolis in EDL muscles. MGO treatment increased mRNA expression of inflammation-related molecules, interleukin (IL)-1β, IL-6, and toll-like receptor 4 (TLR4). Brazilian propolis ingestion suppressed these increases. MGO and/or propolis exerted no effect on the accumulation of AGEs, glyoxalase 1 activity, and inflammatory responses in soleus muscles. These results sugges<sup>t</sup> that Brazilian propolis exerts a protective effect against glycation stress by inhibiting the accumulation of AGEs, promoting MGO detoxification, and reducing proinflammatory responses in the skeletal muscle. However, these anti-glycation effects does not lead to prevent glycation-induced muscle mass reduction.

**Keywords:** advanced glycation end products; anti-glycation; glycative stress; glyoxalase; methylglyoxal; cytokine
