Guyz i was wondering if i can have end to end vPC feature enabled between 3850 connected to 2 x 4500 and each 4500 has 2 uplinks to 2 Nexus7k , how can i have all the links to be fowarding in that case
While the Catalyst 4500-X doesn't support vPC it does support the Cisco Virtual Switching System (VSS). If you establish a vPC domain on the Nexus 7K and a VSS switch domain on the Catalyst 4500-X you should be able to achieve an environment where all your links are forwarding.
As a start there's a step-by-step guide at Virtual Switching System (VSS) Configuration For Cisco 4500 series switches that should help with the Catalyst configuration.
Additionally there's the Cisco Catalyst 6500 VSS and Cisco Nexus 7000 vPC Interoperability and Best Practices white paper that has more details on exactly what you're trying to achieve. While it's written for Catalyst 6500, the principles will be the same.