Is δ-Aminolevulinic Acid Dehydratase Rate Limiting in Heme Biosynthesis Following Exposure of Cells to δ-Aminolevulinic Acid?¶

Abstract

Understanding the regulation and control of heme/porphyrin biosynthesis is critical for the optimization of the ␦-aminolevulinic-acid (ALA)-mediated photodynamic therapy of cancer, in which endogenously produced protoporphyrin IX (PPIX) is the photosensitizer. The human breast cancer cell line MCF-7, the rat mammary adenocarcinoma cell line R3230AC, the mouse mammary tumor cell line EMT-6 and the human mesothelioma cell line H-MESO-1 were used to study ALA-induced PPIX levels and their relationship to ␦-aminolevulinic acid dehydratase (ALA-D) activity in vitro. Incubation of these cell lines with 0.5 mM ALA for 3 h resulted in a significant increase in PPIX accumulation, compared with control cells, but there was no significant change in ALA-D activity. Exposure of cells incubated with ALA to 30 mJ/ cm 2 of fluorescent light, a dose that would cause a 50% reduction in cell proliferation, did not significantly alter the activity of ALA-D. Increasing the activity of porphobilinogen deaminase (PBGD), the enzyme immediately subsequent to ALA-D, by four-to seven-fold via transfection of cells with PBGD complementary DNA did not alter the activity of ALA-D. However, incubation of cells with various concentrations of succinyl acetone, a potent inhibitor of ALA-D, caused a concomitant decline in both PPIX accumulation and ALA-D activity. These data imply that when cells are exposed to exogenous ALA, ALA-D is an important early-control step in heme/porphyrin biosynthesis and that regulation of PPIX synthesis by this dehydratase may impact the effectiveness of ALA-mediated photosensitization.

Metabolic comparison of aerial and submerged mycelia formed in the liquid surface culture of Cordyceps militaris

“…Nevertheless, the expression of CPO was downregulated at 19th day. Interestingly, the expression level of ALAD was the highest among the others and consistent with a previous study of ALAD, which is hypothesized to play a role as the rate limiting step of heme biosynthesis in N. crassa (Chandrika & Padmanaban, ; Gibson, Havens, Metz, & Hilf, ). The putative flavohemoprotein (CCM_5119), which requires heme for its activity, was specifically expressed in the submerged mycelia following 12 days of culture.…”

Review of Neurosurgical Fluorescence Imaging Methodologies

“…Although much of past research points to porphobilinogen deaminase (PBGD) as the rate limiting enzyme in the ALA-PpIX pathway [13, 26], recent research suggests that PBGD may play a minor role in the accumulation of PpIX in vitro [27–29]. Additionally, it has been suggested that ALA-dehydratase, which converts ALA to porphobilinogen, may act as the rate-limiting step as its inhibition causes decreased PpIX production [30]. Moreover, the ferrochelatase enzyme that catalyzes the insertion of iron to convert PpIX to heme is thought to have decreased activity in neoplastic cells, allowing selective accumulation of PpIX in these cells [13, 31].…”

Kinetic Evaluation of Determinant Factors for Cellular Accumulation of Protoporphyrin IX Induced by External 5-Aminolevulinic Acid for Photodynamic Cancer Therapy

“…A deficiency of ferrochelatase (Fc), which catalyzes insertion of Fe 2+ to PPIX, causes intracellular accumulation of PPIX, when ALA is administered externally. Besides, conversion of ALA to porphobilinogen by ALA dehydratase and deamination of porphobilinogen into hydroxymethylbilane by porphobilinogen deaminase (PBGD) could be rate‐limiting steps . Hence, conversion rate of ALA to PPIX is considered as a key element of first‐order multiple compartment models, in which dose‐dependent kinetic constants obtained from in vivo pharmacokinetic studies are incorporated with Michaelis–Menten equation, to predict therapeutic efficacy of ALA in PDT .…”