The influence of iron chelators on the accumulation of protoporphyrin IX in 5-aminolaevulinic acid-treated cells

Human adenocarcinoma cells of the line WiDr and Chinese hamster lung fibroblasts of the line V79 were treated with 5-aminolaevulinic acid (5-ALA) and exposed to light. The effects of the iron chelators ethylenediaminetetraacetic acid (EDTA) and desferrioxamine (DEF) were assessed. Both cell lines were treated with various concentrations of 5-ALA in the presence or absence of the iron chelators for 4 h in serum-free medium. The accumulation of protoporphyrin IX (PpIX) reached a maximum level at 1 mM 5-ALA in WiDr cells [280 ng PpIX (mg protein x 4 h-1] and at 0.1 mM 5-ALA in V79 cells [55 ng PpIX (mg protein x 4 h)-1]. PpIX was the only fluorescing porphyrin in these cells after 5-ALA treatment alone or in combination with the chelators. The iron chelators did not influence the intracellular localisation pattern of PpIX in 5-ALA-treated cells. While both chelators enhanced the accumulation of PpIX in 5-ALA-treated cells, DEF was found to be superior at equal concentrations. A linear relationship between the applied concentration of DEF and the DEF-induced increase in PpIX accumulation was observed in double-reciprocal plots. The intercepts of the regression lines with the ordinate indicate that the ferrochelatase is saturated with PpIX when the 5-ALA concentration exceeds 0.3 mM and 0.05 mM in WiDr and V79 cells respectively. The DEF-induced enhancement of PpIX accumulation in 5-ALA-treated cells was cell line and 5-ALA concentration dependent. At a 5-ALA concentration inducing a maximum level of PpIX accumulation, inhibition of ferrochelatase activity enhanced the PpIX accumulation 3- and 1.4-fold in V79 and WiDr cells respectively. The relative gain in PpIX accumulation increased with decreasing concentration of 5-ALA. In cells treated with the lowest concentrations of 5-ALA used in this study, DEF enhanced PpIX accumulation 44- and 3.5-fold in V79 and WiDr cells respectively. The iron chelator-induced increase in cellular PpIX accumulation was followed by a similar increase in sensitivity to photoinactivation. The ferrochelatase inhibitor dihydropyridine 3,5-diethoxycarbonyl-1,4-dihydrocollidine reduced the accumulation of PpIX in both cell lines.

Photobleaching of protoporphyrin IX in cells incubated with 5-aminolevulinic acid

Protoporphyrin IX (Pp IX) is the main photosensitizer in photochemotherapy with 5-aminolevulinic acid (ALA). Pp IX is photolabile and the present work shows that 70-95% of Pp IX in cells is degraded by clinically relevant light exposures (40-200 J cm(-2) at 630 nm). During light exposure a small yield of photoprotoporphyrin, which is also photolabile, is formed. A substantial fraction of Pp IX in cells incubated with ALA is bound to proteins. During light exposure these binding sites are destroyed, those close to tryptophan residues being the most sensitive. The rate of photodegradation of Pp IX in the cells is dependent on the initial concentration of Pp IX. The degradation mechanisms are therefore not only first order processes. Different degradation rates appear to be related to different types of binding sites. During light exposure, Pp IX molecules appear to move to different binding sites, evidently sites that are more vital for cell survival. Thus, the yield of photoinactivation of the cells, as measured per emitted photon of Pp IX fluorescence, increased during light exposure.

Protoporphyrin IX accumulation in cells treated with 5-aminolevulinic acid: dependence on cell density, cell size and cell cycle

Human colon adenocarcinoma cells (WiDr) and Chinese hamster lung fibroblasts cells (V79) were incubated with different concentrations of 5-aminolevulinic acid (ALA), and the production of protoporphyrin IX (PpIX) was studied using several techniques. The amount of PpIX produced per cell increased with increasing ALA concentration according to different kinetics for the 2 cell lines. For both cell lines a cell density dependency of the PpIX synthesis was observed. For saturating ALA concentrations, 2-3 times more PpIX was produced per cell at a density of 5 x 10(4) than at a density of 5 x 10(3) cells/cm2. The photosensitivity of cells appeared to increase even more than the PpIX content, indicating a cooperative effect in inactivation. The PpIX production rate increased with cell size and was about 1.9 times higher for cells in the G2 + M phase than for cells in the G1 phase of the cell cycle. Neither cell size nor cell cycle distribution were significantly dependent on cell density.

Improvements in quality of life associated with insulin analogue therapies in people with type 2 diabetes: results from the A1chieve observational study

AIMS

To determine the effects on quality of life after starting insulin with, or switching to, insulin analogue therapies in the 24-week, prospective, non-interventional, observational A(1)chieve study conducted across four continents in people with type 2 diabetes.

METHODS

Health-related quality of life (HRQoL) was assessed at baseline and at 24 weeks by the validated EQ-5D questionnaire (visual analogue score [VAS] and five dimensions) in 66,726 people who had started using basal insulin detemir, mealtime insulin aspart (with or without a basal insulin) or biphasic insulin aspart 30.

RESULTS

For the overall cohort, reported HRQoL increased significantly by 13.8 points from 63.4 points at baseline to 77.2 points at 24 weeks (p<0.001) (scale 1-100, 100=best health imaginable). Beginning or changing insulin was associated with a significant increase in HRQoL score (+15.0 points and +11.1 points, respectively), resulting in a similar score at 24 weeks in the two populations (77.8 and 75.9 points). Reported HRQoL also increased statistically significantly in people administering any insulin analogue regimen and across all regions, although there were some marked regional differences in reported HRQoL at baseline.

CONCLUSION

Compared with baseline scores, beginning insulin with, or switching to, insulin analogue therapies are associated with increased HRQoL.

A hydroxypyridinone (CP94) enhances protoporphyrin IX formation in 5-aminolaevulinic acid treated cells

Different cell lines were given photodynamic treatment with 5-aminolaevulinic acid (ALA) and light. In addition, the iron chelator 1,2-diethyl-3-hydroxypyridin-4-one (CP94) was used. The porphyrin species produced was spectrofluorimetrically identified as protoporphyrin IX. All the cell lines responded to treatment, including a multidrug resistance gene expressing bladder cancer line and, to a lesser degree, cells derived from untransformed human skin fibroblasts. CP94 enhanced both porphyrin fluorescence, total porphyrin content and photosensitivity of the cells. CCD fluorescence microscopy showed a granular extranuclear porphyrin fluorescence distribution for all the cell lines involved, but the untransformed cells showed a distribution pattern different from the ones seen in the other cells.

The pH dependency of protoporphyrin IX formation in cells incubated with 5-aminolevulinic acid

Chinese hamster cells (V79) and human adenocarcinoma cells (WiDr) were incubated with 5-aminolevulinic acid (ALA) at different pH values and the rate of production of protoporphyrin IX (PpIX) was measured. The rate of production increased with pH in the range 6.0-7.5. Above pH 7.5 the rate decreased, possibly due to a reduced metabolic activity of the cells. The observations may be explained by the known pH-dependency of the activity of porphobilinogen deaminase (PBGD) and are in agreement with the assumption that PBGD constitutes a rate-limiting step in the synthesis of PpIX from ALA.

[Use of 5-aminolevulinic acid in photochemotherapy and fluorescence diagnostics]

5-aminolevulinic acid is an early intermediate product in the synthesis of heme. Some of the enzymes in the heme synthesis chain have altered activities in tumor tissue, so that application of 5-aminolevulinic acid leads to an accumulation of protoporphyrin IX in tumors. This molecule absorbs light and acts as a potent photosensitizer; tumors containing the compound can therefore be destroyed by light. 5-aminolevulinic acid based photochemotherapy is presently being employed in the treatment of thin basal cell carcinomas in many countries. The cosmetic result of this treatment is excellent. Furthermore, it is a simple and inexpensive form of treatment with curative rates comparable to those of established therapy modalities. Experimentally, a number of other malignant lesions reachable by light via optical fibers are being treated. Since protoporphyrin IX has a characteristic red fluorescence, 5-aminolevulinic acid can also be applied for diagnostic purposes.