It is unclear whether this negative metabolic effect was due to: reduced endothelial function in densely populated, viable GCs; substrate limitation in vitro; or to a direct effect of metformin on cells.
Experimental studies have shown that Legionella spp. are affected by osmolarity (35 ) and metal concentration (36 ) and that iron limitation in vitro reduces bacteria growth and expression of the zinc-metalloprotease that is an important pathogenicity factor (37 ).
Despite this limitation, in vitro models with human immortalized cell lines possess several advantages and may be favorable tools for obtaining first mechanistic insights into BBB permeability of drugs.
This limitations of in-vitro studies using plastic femora or artificial molds have been pointed out previously (McCaskie et al. 1997, Munro et al. 2007).
However, we believe that regulators at a certain, not too distant, point (as discussed below) will accept the inherent limitations of in vitro testing in the same way as they currently accept the limitations of in vivo testing.
The limitations of in vitro experimentation in understanding biofilms and chronic infection.
However, there are numbers of limitations for in vitro cell proliferation.
However, none is entirely satisfactory owing to the inherent limitations of in vitro studies of histones, such as deficits in the knowledge of the proteins involved, and the associated difficulties in the consistent and quantitative generation of histone marks.
