Histoquantitative teratogenic effects of prenatal exposure to tetracycline on fetal skeletogenesis in Albino rats (Rattus norvegicus)

Abstract

The bone teratogenic effects of tetracycline group of medicines following in-utero exposure has been contentious of late in that doxycline and minocycline have been shown to enhance bone formation in low doses. This is contrary to the documented bone calcium chelation effect of tetracycline’s. The broad objective of this study therefore was to evaluate the histoquantitative and histomorphological teratogenic effects of tetracycline on fetal skeletogenesis upon exposure to varied doses of tetracycline at different gestational periods in Albino rats (Rattus novegicus). In carrying out this study, 30 Albino rat dams weighing between 200-250g were used. The 30 dams were grouped into 3 control group and 27 experimental group rats which were further grouped into 3 different groups each having 9 rats to receive tetracycline over different durations. The 9 rats were further subdivided into 3 different dosing categories as Low (155mg/kg/day), Medium(232mg/kg/day) and High dose (310mg/kg/day) tetracycline groups. Confirmation of pregnancy marked the 1st day of pregnancy, treatment began and animals sacrificed on day 20 of gestation using concentrated CO2 and fetuses harvested. Gross morphometric measurements were done using a digital Vanier calipers while photomicrographs were analyzed using Image J v1.50i© stereological software after tissue processing and H&E staining. Fetuses for gross qualitative analysis were processed using the Christiene Effting protocol and examined using Leica M205C Stereomicroscope. Data was captured in MS Excel spreadsheets and analyzed using SPSS v25. One-way ANOVA and Pearson Chi square were used in statistical analysis with statistical significance set at p˂0.05. The study findings showed a statistically significant difference (p<0.05) in the ratio of hypertrophic zone to primary spongiosa which was observed more in the medium (232.5mg/kg) and high dose (310mg/kg) tetracycline groups irrespective of duration of exposure. In addition, a statistically significant (p<0.05) dose dependent reduction in crown rump length and biparietal diameter was observed in the medium and high dose tetracycline treatment groups with the reduction shown not to be influenced by duration of exposure to tetracycline. Similar findings were also noted for rib anomalies and ossification status (p<0.05) whereby rats that received high and medium dose tetracycline had wavy ribs, incomplete ossification and unossification and this as well was not influenced by the duration of exposure to tetracycline. Contrary to these findings, tetracycline was shown not to influence the quantitative histological contribution of the reserve cartilage and proliferation zone to epiphyseal growth plate neither did it influence the tibia length(p>0.05) regardless of the duration of exposure. From the study findings, it can be concluded that the bone chelation effect of tetracycline is dose dependent, with high tetracycline dose having the highest chelation effects followed by medium tetracycline dose whereas at low doses, chelation effects were not realized. These bone chelation effects were found not to be time dependent. From the study it has been shown that low doses of tetracycline maintain bone synthesis. This unique property can be explored for treatment of demineralization disorders.