CTSK and nicotine dependence: For KEGG analysis, CTSK is mainly enriched in pancreatic secretion, starch and sucrose metabolism, protein digestion and absorption, carbohydrate digestion and absorption, salivary secretion, fat digestion and absorption, and glycerolipid metabolism (Figure 7(e)), while PLAU is mainly enriched in pancreatic secretion, protein digestion and absorption, dopaminergic synapse, starch and sucrose metabolism, cholinergic synapse, nicotine addiction, fat digestion and absorption, and synaptic vesicle cycle (Figure 7(g)).