An increasing number of studies demonstrate the ability of peptides to cross the blood-brain
barrier (BBB), opening perspectives for a new class of therapeutics for central nervous system diseases.
However, information on the BBB transport of peptides suffer from a wide variety in used
methods and experimental set-up. Therefore, it is currently difficult, if not impossible, to classify peptides
according to their BBB influx characteristics. To allow direct comparison of BBB influx results
of peptides, we introduce a classification method and unified response for BBB influx transport of peptides. First, the results
of BBB influx response types (i.e. Kin (MTR), Kin (Perfusion), Pin vitro and Pin vivo), which quantitatively express brain
influx, were classified into five classes of BBB influx magnitude based on the distribution of these results for the individual
response types. Then, these classes were converted to a BBBin-response, representing a scaled value ranging from zero
(no influx) to ten (high influx), independent from the BBB influx response type from which it was derived. This unified
response can immediately be applied for new BBB influx results of peptides and represents a ballpark figure for BBB influx
and allows direct comparison and ranking of peptides independent of the response type.