In AIP mice, successive acute attacks did not modify renal function as measured by blood urea nitrogen values (Figure 1C). Figure 1 Lack of glomerular, tubulointerstitial or vascular damage in acute intermittent porphyria mice after excellent validation sustained urinary porphyrin precursors and porphyrin excretion induced by phenobarbital challenge. These animals were sacrificed three days after the last phenobarbital dose of a challenge. The ALAS1 mRNA level was significantly increased in AIP mice when compared with wild type mice, 2.3��1.2 vs 1.0��0.9 Arbitrary Units, respectively; p=0,0498, one-tailed unpaired t-test with Welch’s correction. Histological analysis of kidney tissues from AIP mice and age-matched wild type animals showed lack of porphyrin deposits and no vascular or tubulointerstitial damage (Figure 1C).
Half of the animals from each group exhibited focal accumulations of mononuclear inflammatory cells, mostly in the perivascular space. Light micrographs of kidney sections showed relatively innocuous tubular dilatation in one AIP animal (Figure 1D) and diffuse cortical atrophy in the subcapsular region in another AIP animal (Figure 1E). These changes had no impact on renal function and can occur as a senile change in old wild type animals. These results show that high excretion of porphyrin precursors and porphyrins have little impact on renal function. Mild degrees of renal lesions can occur as a senile change in old animals and seem unrelated to acute attacks of porphyria.
Partial nephrectomy raised urinary PBG/ALA ratio in porphyric animals In a second study, five-sixth nephrectomy was performed in adult wild type and AIP mice after 2/3 nephrectomy of one kidney and extirpation of the other. Other cohorts of mice were sham-operated. Heme precursor excretion were measured before and after phenobarbital challenge (Figure 2A�CC and Table 1). Renal insufficiency caused by 5/6 nephrectomy per se increased in the AIP mice the urinary PBG excretion (Figure 2A, baseline) in male and female, p=0.008 and p=0.007 respectively, compared to values in sham operated AIP mice. No changes were observed in urinary ALA (Figure 2B, baseline) and porphyrin excretion (Table 1). As expected, phenobarbital challenge exacerbated ALAS1 up-regulation and high levels of both porphyrin precursors and porphyrins were found in the urine (Figure 2A and 2B and Table 1), both in sham operated and 5/6 nephrectomized AIP mice of both sexes.
Figure 2 Porphyrin precursor excretion in wild type and AIP mice suffering from different degrees of renal insufficiency. Table 1 Serum cystatine and porphyrin levels in wild type and AIP mice with different degrees of chronic renal failure. Phenobarbital challenge underlined the selective accumulation of PBG in partially nephrectomized animals, as measured by the increased PBG/ALA ratio Batimastat (Figure 2C).