Assessment of the usage of biodegradable polymeric matrix in vaginal devices to sustain progesterone release in cows

Abstract

The usage of timed artificial insemination (TAI) at a low cost leading to better reproductive rates has been the aim of several research groups in the field. Usually during TAI protocols, sustained progesterone (P4 ) release devices are employed. Most devices are constituted of a nylon skeleton covered with a silicon layer with P4 . A device based on biopolymers was developed in order to reduce costs and decrease its environmental impact. In this study, we compared the kinetics of sustained progesterone release among devices manufactured with a polymeric blend made of polyhydroxybutyrate-valerate (PHBV) and poly-ε-caprolactone (PCL) (DISP) which were compared with DIB® (Internal Bovine Device) used as the control. In the in vitro and in vivo progesterone release tests, two types of biopolymer-based devices with a superficial area of 147cm2 were used: DISP8 (46% PHBV, 46% PCL and 8% P4 ; n=4), DISP10 (45% PHBV, 45% PCL, 10% P4 ; n=4) and DIB® (1g P4 , 120cm2 area; n=3). The in vitro tests were carried out according to USP XXIII specifications and were performed in a dissolutor sink using an alcohol/water mixture (60/40v/v) as a release media and samples were collected at 2min, 2, 4, 8, 12, 24, 48, 60, 72, 84 and 96h. P4 concentrations were measured through spectrophotometry in a 244nm long wave. Three to 3 comparisons of angular coefficients of the straight lines obtained by regression analysis of accumulated P4 concentrations as a function of square root of time were carried out. Furthermore, the diffusion coefficient values of P4 were also determined for DISP8 and DISP10. The results showed that the concentrations of P4 were higher in the DISP10 (774.63±45.26μg/cm2 /t1/2 ) compared to DISP8 (566.17±3.68μg/cm2 /t1/2 ) (P<0.05). However, both DISP10 and DISP8 P4 concentrations did not differ from DIB® (677.39±16.13μg/cm2 /t1/2 ). For the analysis of released quantities per day of the in vitro test, four periods were considered: 0-24, 24-48, 48-72 and 72-96h. In the first 24h, DISP8 released significantly less P4 than DISP10 or DIB®, which did not differ among them. Between 24 and 48h, DISP10 released significantly more P4 than DIB®. DISP8 released an intermediate P4 amount and did not differ significantly from DIB® or DISP10. Between 48 and 72h, P4 quantity released by DISP10 was significant higher (P<0.01) than that of DIB® and DISP8, which did not differ among themselves. Between 72 and 96h, DISP10 released significantly more P4 than DIB®, and DISP8 released an intermediate amount which did not differ from DIB® or DISP10 (P<0.01). There was interaction between treatment and time (P=0.0024). The diffusion coefficient values were: 1.36 × 10-8 (cm2 /s) for DISP10 and 1.12 × 10-8 (cm2 /s) for DISP8. For the in vivo test, ovariectomized crossbred cows received DIB® (n=4) or DISP8 (n=8) in an alternate design with a non-balanced sequence (cross-over) added of measures repeated in time referring to 16days of blood samples collection. Samples were analyzed through radioimmunoassay in solid phase using the commercial kit of DPC (Diagnostics Products Corporation). Plasma concentrations of P4 peaked at 4h after the placement of the device, this being the only time in which plasma P4 concentrations differed between DIB® (11.45±1.96) compared with DISP8 (9.23±1.15ng/mL) (P=0.027). On day 8, plasma P4 concentrations were similar for DIB® (2.44±0.09) and DISP8 (1.89±0.13ng/mL) (P=0.58) showing that both devices were able to keep P4 concentrations above 1ng/mL in the plasma of the cow during the 16 day in vivo test. In conclusion, devices manufactured with the blend of PHBV/PCL biopolymers can sustain the release of P4 in a similar manner as silicon.