Both are diffrent product
Topaz is for performance monitoring..it can be used 24X7 for low intrusion monitoring of various infrastructure & server components
LoadRunner is for performance testing
You can use Topaz for perormance monitoring while carrying out performance testing with LoadRunner
With LoadRunner, you are deliberately causing additional load to see how the system responds. For example, 10000 concurrent users with a mix of ten business processes.
With TOPAZ, your goal is to not introduce additional load to impact other users, but to sample at rate sufficient to determine the average user's experience in navigating an application/site/API/etc... For example, one user logging in and checking how long it takes to pull up an account once every ten minutes.