Histidine catabolism is a major determinant of methotrexate sensitivity.

The chemotherapeutic drug methotrexate inhibits the enzyme dihydrofolate reductase1, which generates tetrahydrofolate, an essential cofactor in nucleotide synthesis2. Depletion of tetrahydrofolate causes cell death by suppressing DNA and RNA production3. Although methotrexate is widely used as an anticancer agent and is the subject of over a thousand ongoing clinical trials4, its high toxicity often leads to the premature termination of its use, which reduces its potential efficacy5. To identify genes that modulate the response of cancer cells to methotrexate, we performed a CRISPR-Cas9-based screen6,7. This screen yielded FTCD, which encodes an enzyme-formimidoyltransferase cyclodeaminase-that is required for the catabolism of the amino acid histidine8, a process that has not previously been linked to methotrexate sensitivity. In cultured cancer cells, depletion of several genes in the histidine degradation pathway markedly decreased sensitivity to methotrexate. Mechanistically, histidine catabolism drains the cellular pool of tetrahydrofolate, which is particularly detrimental to methotrexate-treated cells. Moreover, expression of the rate-limiting enzyme in histidine catabolism is associated with methotrexate sensitivity in cancer cell lines and with survival rate in patients. In vivo dietary supplementation of histidine increased flux through the histidine degradation pathway and enhanced the sensitivity of leukaemia xenografts to methotrexate. The histidine degradation pathway markedly influences the sensitivity of cancer cells to methotrexate and may be exploited to improve methotrexate efficacy through a simple dietary intervention.

Molecular genetics of naringenin biosynthesis, a typical plant secondary metabolite produced by Streptomyces clavuligerus.

BACKGROUND: Some types of flavonoid intermediates seemed to be restricted to plants. Naringenin is a typical plant metabolite, that has never been reported to be produced in prokariotes. Naringenin is formed by the action of a chalcone synthase using as starter 4-coumaroyl-CoA, which in dicotyledonous plants derives from phenylalanine by the action of a phenylalanine ammonia lyase. RESULTS: A compound produced by Streptomyces clavuligerus has been identified by LC-MS and NMR as naringenin and coelutes in HPLC with a naringenin standard. Genome mining of S. clavuligerus revealed the presence of a gene for a chalcone synthase (ncs), side by side to a gene encoding a P450 cytochrome (ncyP) and separated from a gene encoding a Pal/Tal ammonia lyase (tal). Deletion of any of these genes results in naringenin non producer mutants. Complementation with the deleted gene restores naringenin production in the transformants. Furthermore, naringenin production increases in cultures supplemented with phenylalanine or tyrosine. CONCLUSION: This is the first time that naringenin is reported to be produced naturally in a prokariote. Interestingly three non-clustered genes are involved in naringenin production, which is unusual for secondary metabolites. A tentative pathway for naringenin biosynthesis has been proposed.

Characterization of the porphobilinogen deaminase deficiency in acute intermittent porphyria. Immunologic evidence for heterogeneity of the genetic defect.

The molecular pathology of the porphobilinogen (PBG)-deaminase deficiency in heterozygotes for acute intermittent porphyria (AIP) was investigated by means of biochemical and immunologic techniques. The stable enzyme-substrate intermediates (A, B, C, D, and E) of PBG-deaminase were separated by anion-exchange chromatography of erythrocyte lysates from heterozygotes for AIP and normal individuals. In normal lysates, the intermediates eluted in a characteristic pattern with decreasing amounts of activity (A > B > C > D > E), the combined A and B intermediates representing >75% of total recovered activity. In contrast, two different profiles were observed in lysates from heterozygotes for AIP. In most heterozygotes, the elution profile was similar to that of normal individuals, but each intermediate was reduced approximately 50%. A second profile in which the C intermediate had disproportionately higher activity than the A or B intermediates was observed in asymptomatic heterozygotes with high urinary levels of PBG (>5 mug/ml) as well as in heterozygotes during acute attacks. These findings suggested that the C intermediate (the dipyrrole-enzyme intermediate) may be rate limiting in the stepwise conversion of the monopyrrole, PBG, to the linear tetrapyrrole, hydroxymethylbilane. To investigate further the nature of the enzymatic defect in AIP, sensitive immunotitration and immunoelectrophoretic assays were developed with the aid of a rabbit anti-human PBG-deaminase IgG preparation produced against the homogeneous enzyme. Equal amounts of erythrocyte lysate activity from 32 heterozygotes for AIP from 22 unrelated families and 35 normal individuals were immunoelectrophoresed. There were no detectable differences in the amounts of cross-reactive immunologic material (CRIM) in lysates from the normal individuals and 25 heterozygotes from 21 of the 22 unrelated families with AIP. In contrast, when equal enzymatic activities were coimmunoelectrophoresed, all seven heterozygotes from one family had approximately 1.6 times the amount of CRIM compared with that detected in normal lysates. Consistent with these findings, immunotitration studies also demonstrated similar quantities of noncatalytic CRIM in lysates from this AIP family. When equal activities of the individual A, B, C, and D enzyme-substrate intermediates from normal and CRIM-positive erythrocytes were immunoelectrophoresed, increased amounts of immunoreactive protein were observed for each intermediate, B > A approximately C approximately D, from the CRIM-positive AIP variants. On the basis of these findings, it is hypothesized that the enzymatic defect in the CRIM-positive AIP family resulted from a mutation in the structural gene for PBG-deaminase which altered the catalytic as well as a substrate binding site. These studies of the enzymatic defect provide the first demonstration of genetic heterogeneity in AIP.

The molecular basis of glutamate formiminotransferase deficiency.

Glutamate formiminotransferase deficiency, an autosomal recessive disorder and the second most common inborn error of folate metabolism, is presumed to be due to defects in the bifunctional enzyme glutamate formiminotransferase-cyclodeaminase (FTCD). Features of a severe phenotype, first identified in patients of Japanese descent, include elevated levels of formiminoglutamate (FIGLU) in the urine in response to histidine administration, megaloblastic anemia, and mental retardation. Features of a mild phenotype include high urinary excretion of FIGLU in the absence of histidine administration, mild developmental delay, and no hematological abnormalities. We found mutations in the human FTCD gene in three patients with putative glutamate formiminotransferase deficiency. Two siblings were heterozygous for missense mutations, c.457C>T (R135C) and c.940G>C (R299P). Mutagenesis of porcine FTCD and expression in E. coli showed that the R135C mutation reduced formiminotransferase activity to 61% of wild-type, whereas the R299P mutation reduced this activity to 57% of wild-type. The third patient was hemizygous for c.1033insG, with quantitative PCR indicating that the other allele contained a deletion. These mutations are the first identified in glutamate formiminotransferase deficiency and demonstrate that mutations in FTCD represent the molecular basis for the mild phenotype of this disease.

[Acute intermittent porphyria at 4 months of age]. / Porphyrie aigue intermittente à l'age de quatre mois

Acute intermittent porphyria was diagnosed in a child who presented with an acute abdomen and neurological signs of the age of four months. The diagnosis was confirmed by the absence of uroporphyrinogen synthetase in the erythrocytes. The rarity of the disorder at this age is emphasised.

[Histidine tolerance in low skin histidase activity]. / Histidintoleranz bei niedriger Haut-Histidaseaktivität

An oral histidine loading test (100 mg L-His/kg body weight) was performed in 8 deaf patients with low histidase activity in the str. corneum of the skin. Beside an elevated plasma phenylalanine level resulting in a Phe/Tyr-quotient of 1,09 +/- 0,15 the basal level of histidine was slightly enhanced in patients with deafness, but without statistical significance. After histidine loading no differences of the histidine tolerance curves could be observed suggesting the heterozygosity state for histidinaemia. Thin-layer chromatographic investigation of imidazole compounds revealed some abnormal findings after loading. The results are discussed with regard to the clinical and biochemical heterogeneity of histidinaemia.

Disturbances in histidine metabolism in children with speech abnormalities.

Catabolism of histidine was investigated in 24 patients with different speech and language disorders and with significantly low histidase activity in stratum corneum. No classical histidinemia was found. Biochemical investigation of these patients after loading with L-histidine led to the conclusions that low histidase activity in stratum corneum was connected with: disturbances in folic acid metabolism (2 cases); "atypical histidinemia" (1 case); heterozygotes of histidinemia (2 cases); normal liver histidine metabolism but abnormal in other tissues (18 cases); previously unknown error of histidine metabolism (1 case).

Zinc status of untreated histidinemic children.

In order to study zinc status in histidinemia, serum and hair zinc concentrations were measured in 40 untreated children with histidinemia (age 2 months-5 years). In 20 children (greater than 2 years of age) zinc content and carbonic anhydrase activity of erythrocytes and urinary excretion of zinc were also studied. The amount of zinc excreted was elevated in histidinemic children and showed a positive correlation with the urinary histidine concentration (gamma = 0.57, p less than 0.005). The means of serum zinc concentration, erythrocyte zinc concentration, and erythrocyte carbonic anhydrase activity were all similar in the histidinemic and the control children. Hair zinc concentration of histidinemic children was compared with that of controls of five different age groups: less than 5 months, 5-18 months, 18 months-2 years, 2-4 years, and 4-5 years. In all of these age groups, hair zinc content was similar. The incidence of low-hair-zinc level (less than 80 micrograms/g) in histidinemic children greater than 5 months of age (9 of 34) was significantly higher than in controls (18 of 180, p less than 0.05). The observation suggested the possibility that untreated histidinemia may cause chronic mild zinc deficiency in some histidinemic children.

Dual porphyria in double heterozygotes with porphobilinogen deaminase and uroporphyrinogen decarboxylase deficiencies.

A coexistent dual deficiency of porphobilinogen deaminase (PBG-D; EC 4.3.1.8) and uroporphyrinogen decarboxylase (EC 4.1.1.37) in erythrocytes was recognized in five individuals, four males and one female. Clinically, the female and one male were diagnosed as suffering from acute intermittent porphyria (AIP), and the other two males were diagnosed as having porphyria cutanea tarda (PCT). Biochemically, the excretion pattern of urinary and fecal heme precursors exhibited a complex constellation with signs characteristic for both AIP and PCT. A coexistent dual enzyme deficiency of PBG-D and URO-D could be confirmed by repeated studies over 10 years. Clinical courses of both disease manifestations were observed. Family investigations have shown that the two disorders do not consistently segregate together. The findings suggest that the dual porphyria reflects a double heterozygous condition of coexistent AIP and PCT genes in the same individual.

An autopsy case of acute porphyria with a decrease of both uroporphyrinogen I synthetase and ferrochelatase activities.

An autopsy case of a 37-year-old woman with acute porphyria is reported. The patient began to complain of severe menstrual pains, and later developed serious peripheral neuropathy and various autonomic nervous symptoms. The autopsy revealed a marked loss and degeneration of axons and myelin sheaths in the peripheral nervous system (PNS), and prominent central chromatolysis of the spinal anterior horn cells. The predominant process of the peripheral neuropathy appeared to be axonal degeneration. Biochemical analysis showed a marked increase of delta-aminolevulinic acid (ALA), porphobilinogen, uroporphyrin, and coproporphyrin in the urine, and an increase of coproporphyrin and protoporphyrin in the stools and blood. In the analysis of the enzymatic activities of the liver and bone narrow, the activity of ALA synthetase (ALA-S) was markedly increased, and the activities of both uroporphyrinogen I synthetase (URO-S) and ferrochelatase were decreased. It was characteristic in this case that the enzymatic abnormalities found in both acute intermittent porphyria (AIP) and variegate porphyria (VP) coexisted. Biochemical analysis of the sciatic nerve showed an increase of ALA-S activity and a decrease of both URO-S and ALA dehydrase activities. This was the first report that indicated the presence of abnormal activities of the heme biosynthetic enzymes in the peripheral nerves of porphyric patients. The possibility was discussed that these enzymatic abnormalities of the heme biosynthesis in the peripheral nerve itself might be strongly related to the pathogenesis of the porphyric neuropathy.

Anesthesia and the porphyrias.

A simplified classification of the porphyrias is given which is thought to be advantageous to the anesthesiologist in determining those patients who are predisposed to acute attacks. These acute attacks may be precipitated by the administration of barbiturates, but may also be spontaneous. The current theory for the precipitation of the acute attack is described, with the probable mechanism being a decrease in uroporphyrinogen synthetase levels and the resultant interference in heme production. Increased formation of cytochrome P-450 with barbiturates also produces increased levels of delta aminolevulinic acid, which may be a cause of the acute attack. The significance in anesthesia and suggested means of anesthetic management are discussed.