Distinctive quality control method for solid-state fermented Isaria cicadae from strain Ic-17-7 and application in a rat model of type 2 diabetes

This work was aimed to establish a quality control method for evaluating the effects on glucose and lipids of the fruiting body of Isaria cicadae Miquel from strain Ic-17-7 (Ic-17-7fb) using a rat model of type 2 diabetes (T2DM). Random amplified polymorphic DNA, sequence-characterized amplified region, and high-performance liquid chromatography (HPLC) were used for the quality control of Ic-17-7fb. The pharmacological effects on streptozocin (STZ)-induced high fat diet (HFD)-fed Albino Wistar rats were evaluated. The rats underwent the following treatments: control, metformin, Ic-17-7fb (0.166 and 0.5 g·kg⁻¹) or without treatment. The fasting blood glucose (FBG), blood glucose, total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL-c), and low-density lipoprotein (LDL-c) were measured. Ic-17-7fb amplified a single specific band by S11-2-F3 and S11-2-R3 primers. An HPLC-based quality and quantity method was established for industrial application. The contents of adenosine and N⁶-(2-hydroxyethyl) adenosine (HEA) of the cultivated Ic-17-7fb were analyzed. All of the validation lots of cultured Ic-17-7fb passed the quantity control of the training set (0.90 mg·g⁻¹ of adenosine and 0.89 mg·g⁻¹ of HEA). After two weeks of administration, the average FBG was 4.89 ± 0.42 (control), 26.10 ± 5.77 (model), 23.63 ± 6.15 (metformin), 17.96 ± 9.36 (Ic-17-7fb for 0.166 g·kg⁻¹), and 19.69 ± 8.71 mmol·L⁻¹ (Ic-17-7fb for 0.5 g·kg⁻¹). The FBG of Ic-17-7fb (0.166 g·kg⁻¹) treatment significantly reduced by 31.19%, compared with the model after two weeks of administration (P < 0.01). Metformin, Ic-17-7fb (0.166 g·kg⁻¹), and Ic-17-7fb (0.5 g·kg⁻¹) reduced TC, TG, HDL-c, and LDL-c compared with the T2DM model treatment at the 6th week of treatment (P < 0.05). This study established the first quality standard for Ic-17-7fb, which can be effectively applied in the treatment of T2DM. The reliable quality control method and pharmacological effect will broaden its application space.