Principal component analysis of metabolites in urine from rats treated with procyanidin A2 and two oligomeric procyanidin fractions from cranberry

Cranberry (Vaccinium macrocarpon) fruits are widely used for the prevention and treatment of urinary tract infections. The mode of action is usually explained with an inhibition of bacterial adherence to the urothelium due to the content of oligomeric procyanidins (OPC) with A-type bonding. However, oral bioavailability of OPC is limited and it is unlikely that they reach the urinary tract as such. Instead, it is assumed that metabolites like procyanidin dimer A2 (PC-A2) or further degraded compounds contribute to the biological effect. Therefore, changes of the urinary metabonom may be helpful for identifying relevant marker substances or even metabolites.

Each four rats were treated orally with vehicle, pure PC-A2 or two OPC fractions with different degrees of polymerization (DP), respectively. Urine samples were collected during defined intervals over a period of 48h. Besides quantification of PC-A2, all further detected signals were characterized by PES-HPLC-MS2. More than 100 signals were identified by mass (m/z), retention time, and area, and were subjected to group comparison by principal component analysis (PCA).

PC-A2 was not bioavailable (LLOQ: 5 ng/mL) when applied in form of the pure compound (50 mg/kg) or an enriched extract (500 mg/kg) containing mainly OPC with a DP about > 6. Interestingly, PC-A2 was detected at a concentration close to LLOQ (6.7 ± 4.8 ng/mL) when given as an extract (500 mg/kg) containing mainly OPC with a low DP (about < 6) including approx. 5% of this dimer. PCA revealed that urine samples from the four different groups clearly separated into distinct clusters applying OPLS-DA classification (SIMCA P version 13).

The results indicate that PC-A2 has a negligible oral bioavailability. While OPC with a higher DP are obviously not metabolized into PC-A2, it cannot be excluded that OPC with a lower DP are metabolized to PC-A2. Thus, the changes in the urinary metabonom observed by PCA are obviously due to other constituents.