Effect of isoniazid on the loss of pyridoxal phosphate from, and its distribution in, the body of the rat

Nutritional peripheral neuropathies

Nutritional peripheral neuropathies are a global problem, heavily influenced by geopolitical, cultural and socioeconomic factors. Peripheral neuropathy occurs most frequently secondary to B-vitamin deficiencies, which is suspected to increase in years to come due to the popularity of vegan and vegetarian diets and increased use of bariatric surgery.This review will focus on the common B-vitamins for which a causal link to peripheral neuropathy is more established (vitamins B1, B2, B6, B9 and B12). We will review the historical human and animal data on which much of the clinical descriptions of vitamin deficiencies are based and summarise current available tools for accurately diagnosing a nutritional deficiency. We will also review recently described genetic diseases due to pathogenic variants in genes involved in B-vitamin metabolism that have helped to inform the phenotypes and potential causality of certain B-vitamins in peripheral neuropathy (B2 and B9).Endemic outbreaks of peripheral neuropathy over the last two centuries have been linked to food shortages and nutritional deficiency. These include outbreaks in Jamaican sugar plantation workers in the nineteenth century (Strachan's syndrome), World War two prisoners of war, Cuban endemic neuropathy and also Tanzanian endemic optic neuropathy, which remains a significant public health burden today. An improved understanding of lack of which vitamins cause peripheral neuropathy and how to identify specific deficiencies may lead to prevention of significant and irreversible disability in vulnerable populations.

Chronological Metabolic Response to Intensive Phase TB Therapy in Patients with Cured and Failed Treatment Outcomes

Despite the arguable success of the standardized tuberculosis (TB) treatment regime, a significant number of patients still present with treatment failure. To improve on current TB treatment strategies, we sought to gain a better understanding of the hosts' response to TB therapy. A targeted metabolomics approach was used to compare the urinary acylcarnitine and amino acid profiles of eventually cured TB patients with those of patients presenting with a failed treatment outcome, comparing these patient groups at the time of diagnosis and at weeks 1, 2, and 4 of treatment. Among the significant metabolites identified were histidine, isoleucine, leucine, methionine, valine, proline, tyrosine, alanine, serine, and γ-aminobutyric acid. In general, metabolite fluctuations in time followed a similar pattern for both groups for most compounds but with a delayed onset or shift of the pattern in the successfully treated patient group. These time-trends detected in both groups could potentially be ascribed to a vitamin B6 deficiency and fluctuations in the oxidative stress levels and urea cycle intermediates, linked to the drug-induced inhibition and stimulation of various enzymes. The earlier onset of observed trends in the failed patients is proposed to relate to genotypic and phenotypic variations in drug metabolizing enzymes, subsequently leading to a poor treatment efficiency either due to the rise of adverse drug reactions or to insufficient concentrations of the active drug metabolites. This study emphasizes the need for a more personalized TB treatment approach, by including enzyme phenotyping and the monitoring of oxidative stress and vitamin B6 levels, for example.

Toxicoproteomic Profiling of hPXR Transgenic Mice Treated with Rifampicin and Isoniazid

Tuberculosis is a global health threat that affects millions of people every year, and treatment-limiting toxicity remains a considerable source of treatment failure. Recent reports have characterized the nature of hPXR-mediated hepatotoxicity and the systemic toxicity of antitubercular drugs. The antitubercular drug isoniazid plays a role in such pathologic states as acute intermittent porphyria, anemia, hepatotoxicity, hypercoagulable states (deep vein thrombosis, pulmonary embolism, or ischemic stroke), pellagra (vitamin B₃ deficiency), peripheral neuropathy, and vitamin B₆ deficiency. However, the mechanisms by which isoniazid administration leads to these states are unclear. To elucidate the mechanism of rifampicin- and isoniazid-induced liver and systemic injury, we performed tandem mass tag mass spectrometry-based proteomic screening of mPxr^-/- and hPXR mice treated with combinations of rifampicin and isoniazid. Proteomic profiling analysis suggested that the hPXR liver proteome is affected by antitubercular therapy to disrupt [Fe-S] cluster assembly machinery, [2Fe-2S] cluster-containing proteins, cytochrome P450 enzymes, heme biosynthesis, homocysteine catabolism, oxidative stress responses, vitamin B₃ metabolism, and vitamin B₆ metabolism. These novel findings provide insight into the etiology of some of these processes and potential targets for subsequent investigations. Data are available via ProteomeXchange with identifier PXD019505.

The Isoniazid Metabolites Hydrazine and Pyridoxal Isonicotinoyl Hydrazone Modulate Heme Biosynthesis

In a mouse model, rifampicin and isoniazid combination treatment results in cholestatic liver injury that is associated with an increase in protoporphyrin IX, the penultimate heme precursor. Both ferrochelatase (FECH/Fech) and aminolevulinic acid synthase 1 (ALAS1/Alas1) are crucial enzymes in regulating heme biosynthesis. Isoniazid has recently been reported to upregulate Alas1 but downregulate Fech protein levels in mice; however, the mechanism by which isoniazid mediates disruption of heme synthesis has been unclear. Two metabolites of isoniazid, pyridoxal isonicotinoyl hydrazone (PIH, the isoniazid-vitamin B6 conjugate) and hydrazine, have been detected in the urine of humans treated with isoniazid. Here we show that, in primary human hepatocytes and the human hepatocellular carcinoma cell line HepG2/C3A, (1) isoniazid treatment increases Alas1 protein levels but decreases Fech levels; (2) hydrazine treatment upregulates Alas1 protein and Alas1 mRNA levels; (3) PIH treatment decreases Fech protein levels, but not Fech mRNA levels; and (4) PIH is detected after isoniazid treatment, with levels increasing further when exogenous vitamin B6 analogs are coadministered. In addition, the PIH-mediated downregulation of human FECH is associated with iron chelation. Together, these data demonstrate that hydrazine upregulates ALAS1, whereas PIH downregulates FECH, suggesting that the metabolites of isoniazid mediate its disruption of heme biosynthesis by contributing to protoporphyrin IX accumulation.

Isoniazid metabolism and hepatotoxicity

Isoniazid (INH) is highly effective for the management of tuberculosis. However, it can cause liver injury and even liver failure. INH metabolism has been thought to be associated with INH-induced liver injury. This review summarized the metabolic pathways of INH and discussed their associations with INH-induced liver injury.

Role of pyridoxal phosphate in mammalian polyamine biosynthesis. Lack of requirement for mammalian S-adenosylmethionine decarboxylase activity

1. Polyamine concentrations were decreased in rats fed on a diet deficient in vitamin B-6. 2. Ornithine decarboxylase activity was decreased by vitamin B-6 deficiency when assayed in tissue extracts without addition of pyridoxal phosphate, but was greater than in control extracts when pyridoxal phosphate was present in saturating amounts. 3. In contrast, the activity of S-adenosylmethionine decarboxylase was not enhanced by pyridoxal phosphate addition even when dialysed extracts were prepared from tissues of young rats suckled by mothers fed on the vitamin B-6-deficient diet. 4. S-Adenosylmethionine decarboxylase activities were increased by administration of methylglyoxal bis(guanylhydrazone) (1,1'-[(methylethanediylidine)dinitrilo]diguanidine) to similar extents in both control and vitamin B-6-deficient animals. 5. The spectrum of highly purified liver S-adenosylmethionine decarboxylase did not indicate the presence of pyridoxal phosphate. After inactivation of the enzyme by reaction with NaB3H4, radioactivity was incorporated into the enzyme, but was not present as a reduced derivative of pyridoxal phosphate. 6. It is concluded that the decreased concentrations of polyamines in rats fed on a diet containing vitamin B-6 may be due to decreased activity or ornithine decarboxylase or may be caused by an unknown mechanism responding to growth retardation produced by the vitamin deficiency. In either case, measurements of S-adenosylmethionine decarboxylase and ornithine decarboxylase activity under optimum conditions in vitro do not correlate with the polyamine concentrations in vivo.

Stable multisubstrate adducts as enzyme inhibitors. Potent inhibition of ornithine decarboxylase by N-(5'-phosphopyridoxyl)-ornithine

The synthesis of several N-(5'-phosphopyridoxyl)-amino acids is described. These compounds, analogs of the Schiff base intermediate involved in enzyme-catalyzed decarboxylation, are potent inhibitors of the cognate amino acid decarboxylases. Kinetic studies using partially purified rat liver ornithine decarboxylase, have shown that N-(5'-phosphopyridoxyl)-ornithine inhibits the enzyme in a non-competitive manner with respect to both ornithine and pyridoxal-5'-phosphate. These findings suggest that the inhibitor binds to the holoenzyme active site in place of the Schiff base intermediate.