Ameliorative effect of berberine on high-fat diet/streptozotocin-induced early diabetic nephropathy in rats

OBJECTIVE To investigate possible protective effect of berberine,an isoquinoline alkaloid,is the major active constituent of Rhizoma coptidis and Cortex phellodendri,on high-fat diet/streptozotocin-induced early diabetic nephropathy in rats and various mechanisms underlie this effect.METHODS The diabetic rat model was generated by a single intraperitoneal injection of streptozotocin(STZ,50 mg·kg-1).Diabetic rats were randomlyassigned into the following five groups:control,DN,losartan(30 mg·kg-1·d-1),berberine(100,200 mg·kg-1·d-1).Berberine and losartan were given intragastricly for nine weeks.At the end of the experiment,urine of each group was collected in a 24 h period.Rats were weighed and then sacrificed.Plasma and kidneys were collected.The levels of blood glucose,creatinine(Cr),triglycerides(TG),total cholesterol(TCH)and malondialdehyde(MDA)in serum were determined using commercial kits according to the manufacturer′s instructions.Transforming growth factor(TGF)-β1and intracellular adhesion molecule-1(IAM-1)mR NA levels were evaluated by RT-PCR.The renal histopathology was observed by light microscopy.Further biochemical analysis of IKKβ1 and p65(nucleus/cytoplasm)was provided using Western blotting techniques.RESULTS Our study has demonstrated that berberine has various pharmacological activities.The DN rats had significantly higher kidney/body weight ratio(17.4±1.4)mg·g-1,and berberine treatment could reduce this ratio change 13.6±0.6 and(11.6±0.8)mg·g-1,respectively;glucose control still remains the only disease-modifying therapy for diabetic complications,FBG was also recorded in the experiment.The findings reveal that the DN group showed a significantly higher glucose level(28.67±2.78)mmol·L-1.Treatment with8 weeks of berberine improved these parameters except blood glucose〔(18.67±2.59)mmol·L-1and 16.45±1.80 vs(28.67±2.78)mmol·L-1:plasma levels of urea nitrogen(15.67±2.48)mmol·L-1and 14.45±2.40 vs(12.26±2.40)mmol·L-1〕;plasma levels of 24 h urine albuminuria〔30.48±1.56 and 25.72±2.24 vs(15.26±0.12)μg·d-1〕;based on these results,berberine supposed to improve renal functions in diabetic rats.Berberine also ameliorated the inflammatory changes of DN in diabetic animals;levels of TG,TCH and MDA in berberine-treatment rats were significantly lower compared with those in the DN group:TG〔2.78±0.24 and 2.45±0.36 vs(5.20±0.60)mmol·L-1〕;TCH〔4.26±0.46 and 3.74±0.68 vs(6.26±0.50)mmol·L-1〕;MDA〔4.94±1.19 and 4.28±0.64 vs(4.28±0.64)nu·mL-1〕.Chronic inflammation,as is observed in diabetes,is associated with increased production of TGF-β1and IAM-1.Compared with the renal tissues of DN group,TGF-β1and IAM-1 gene expressions in berberine treated groups were reduced at the dose levels(100 and 200 mg·kg-1).And TGF-β1and IAM-1levels in berberine treated groups were reduced in a dosedependent manner:Relative expression of TGF-β1mR NA level(3.56±0.28 and 3.12±0.14 vs 5.12±0.44);Relative expression of IAM-1 mR NA leve(l1.78±0.56 and 1.42±0.24vs 4.36±0.35).Research finds that the NF-κB signaling pathway is activated in the renal tissue of diabetic mice and berberine inhibits activation of the NF-κB pathway:staining score for IKKβ1(4.34±0.26 and 3.82±0.24 vs 6.23±0.76),staining score for p65(2.34±0.26 and 1.74±0.78 vs 6.23±0.24)in nucleus and staining score for p65(7.21±0.13 and8.15±0.45 vs 4.23±0.54)in cytoplasm.CONCLUSION In this field,berberine suppresses the increased expression of p65 in the nucleus and decreases it in cytoplasm,which leads to the inhibition of the NF-κB pathway.These changes will result in decreasing the transcription and translation of many inflammatory mediators,such as TGF-β1and IAM-1.Additionally,these changes decrease the number of inflammatory cells and mononuclear macrophage infiltration into glomeruli and renal interstitium.These results indicated that berberine can protect the kidney of STZ-diabetic rats by reducing the expression of TGF-β1and IAM-1 in the renal tubulointerstitium.And we propose that berberinemayfunction as an effective therapeutic agent for diabetic nephropathy and attenuate the progression of renal injury.