In this study, the biodistribution of 5-aminolaevulinic acid (ALA) and accumulation of protoporphyrin IX (PpIX) in rats have been examined. Two groups of 21 WAG/Rij rats are given 200 mg/kg ALA orally or intravenously. Six rats serve as controls. At 1, 2, 3, 4, 6, 12 and 24 h after ALA administration, ALA and porphyrin concentrations are measured in 18 tissues and fluids. Liver enzymes and renal-function tests are measured to determine ALA toxicity. In both groups ALA concentration is highest in kidney, bladder and urine. After oral administration, high concentrations are also found in duodenal aspirate and jejunum. Mild, short-lasting elevation of creatinine is seen in both treatment groups. Porphyrins, especially PpIX, accumulate mainly in duodenal aspirate, jejunum, liver and kidney (> 10 nmol/g tissue), less in oesophagus, stomach, colon, spleen, bladder, heart, lung and nerve (2-10 nmol/g tissue), and only slightly in plasma, muscle, fat, skin and brain (< 2 nmol/g tissue). In situ synthesis of porphyrins rather than enterohepatic circulation contributes to the PpIX accumulation. Confocal laser scanning microscopy shows selective porphyrin fluorescence in epithelial layers. Peak levels and total production of porphyrins are equal after oral and intravenous ALA administration.
In conclusion: administration of 200 mg/kg ALA results in accumulation of photosensitive concentrations of PpIX, 1 to 6 h after ALA administration, in all tissues except muscle, fat, skin and brain. Knowledge of the time-concentration relationship should be helpful in selecting dosages, routes of administration and timing of ALA photodynamic therapy.