PPIG and infection: Most precipitating factors not only directly increase transcription of hepatic ALAS1 [4,5,6] but also increase the demand for heme, either by increasing the production of cytochrome P450 (CYP) hemoenzymes (e.g., hormonal fluctuations [7,8] and CYP-inducing drugs) or by inducing the hepatic expression of the heme-degrading enzyme heme oxygenase (HO) (e.g., in fasting [9,10] and infection [11,12]).