The invention provides a compound which is a polyunsaturated fatty acid (PUFA) derivative of formula (I),or a pharmaceutically acceptable salt, or solvate thereof, wherein- -Alk- is -CH(OR2)-[trans]CH=CH-[cis]CH=CH-CH2-[cis]CH=CH-C3H6-,-(CH2)3-CH(OR2)-[trans]CH=CH-[cis]CH=CH-CH2-[cis]CH=CH-, -(CH2)3-[cis]CH=CH-CH2-[cis]CH=CH-[trans]CH=CH-CH(OR2)- or -CH2-[cis]CH=CH-CH2-[cis]CH=CH-[trans]CH=CH-CH(OR2)-；- R1 is a hydrogen atom； orR1 is a C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C6-C10 aryl, 5- to 10-membered heteroaryl, C3-C7 carbocyclyl or 5- to 10-membered heterocyclyl group； or R1 is a group of formula -CH2-CH(OR3)-CH2-(OR4), wherein R3 and R4 are each independently hydrogen atoms or -(C=O)-R6, wherein R6 is an aliphatic group having from 3 to 29 carbon atoms； orR1 is a group of formula -(CH2OCH2)mOH, wherein m is an integer of from 1 to 200；- R2 is a hydrogen atom； orR2 is a group -(C=O)-R5, wherein R5 is a C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C6-C10 aryl, 5- to 10-membered heteroaryl, C3-C7 carbocyclyl or 5- to 10-membered heterocyclyl group, or R5 is an aliphatic group having from 3 to 29 carbon atoms； orR2 is a group of formula -(CH2OCH2)nOH, wherein n is an integer of from 1 to 200；and wherein- said alkyl, alkenyl, alkynyl and aliphatic groups are the same or different and are each unsubstituted or substituted with 1, 2 or 3 unsubstituted substituents which are the same or different and are selected from halogen atoms and C1-C4 alkoxy, C2-C4 alkenyloxy, C1-C4 haloalkyl, C2-C4 haloalkenyl, C1-C4 haloalkoxy, C2-C4 haloalkenyloxy, hydroxyl, -SR', and -NR'R" groups where R' and R" are the same or different and represent hydrogen or unsubstituted C1-C2 alkyl；- said aryl, heteroaryl, carbocyclyl and heterocyclyl groups are the same or different and are each unsubstituted or substituted by 1, 2, 3 or 4 unsubstituted substituents which are the same or different and are selected from halogen atoms, and cyano, nitro, C
