Delta-Aminolaevulinic acid and amino acid neurotransmitters

Pathogenesis of acute encephalopathy in acute hepatic porphyria

Acute encephalopathy (AE) can be a manifestation of an acute porphyric attack. Clinical data were studied in 32 patients during AE with or without polyneuropathy (PNP) together with 12 subjects with PNP but no AE, and 17 with dysautonomia solely. Brain neuroimaging was done in 20 attacks during AE, and PEPT2 polymorphisms were studied in 56 subjects, 24 with AE. AE manifested as a triad of seizures, confusion and/or blurred vision. Symptoms lasting 1-5 days manifested 3-19 days from the onset of an attack. 55% of these patients had acute PNP independent of AE. Posterior reversible encephalopathy syndrome (PRES) was detected in 42% of the attacks. These patients were severely affected and hyponatremic (88%). Reversible segmental vasoconstriction was rare. There was no statistical difference in hypertension or urinary excretion of porphyrin precursors among the patients with or without AE. In 94% of the attacks with AE, liver transaminases were elevated significantly (1.5 to fivefold, P = 0.034) compared to a normal level in 87% of the attacks with dysautonomia, or in 25% of patients with PNP solely. PEPT2*2/2 haplotype was less common among patients with AE than without (8.3% vs. 25.8%, P = 0.159) and in patients with PNP than without (9.5% vs. 22.9%, P = 0.207), suggesting a minor role, if any, in acute neurotoxicity. In contrast, PEPT2*2/2 haplotype was commoner among patients with chronic kidney disease (P = 0.192). Acute endothelial dysfunction in porphyric encephalopathy could be explained by a combination of abrupt hypertension, SIADH, and acute metabolic and inflammatory factors of hepatic origin.

Cutting-Edge Therapies and Novel Strategies for Acute Intermittent Porphyria: Step-by-Step towards the Solution

Acute intermittent porphyria (AIP) is an autosomal dominant disease caused by the hepatic deficiency of porphobilinogen deaminase (PBGD) and the slowdown of heme biosynthesis. AIP symptomatology includes life-threatening, acute neurovisceral or neuropsychiatric attacks manifesting in response to precipitating factors. The latter promote the upregulation of 5-aminolevulinic acid synthase-1 (ALAS1), the first enzyme of heme biosynthesis, which promotes the overload of neurotoxic porphyrin precursors. Hemin or glucose infusions are the first-line therapies for the reduction of ALAS1 levels in patients with mild to severe AIP, while liver transplantation is the only curative treatment for refractory patients. Recently, the RNA-interference against ALAS1 was approved as a treatment for adult and adolescent patients with AIP. These emerging therapies aim to substitute dysfunctional PBGD with adeno-associated vectors for genome editing, human PBGD mRNA encapsulated in lipid nanoparticles, or PBGD protein linked to apolipoprotein A1. Finally, the impairment of glucose metabolism linked to insulin resistance, and mitochondrial aberrations during AIP pathophysiology provided new therapeutic targets. Therefore, the use of liver-targeted insulin and insulin-mimetics such as α-lipoic acid may be useful for overcoming metabolic dysfunction in these subjects. Herein, the present review aims to provide an overview of AIP pathophysiology and management, focusing on conventional and recent therapeutical approaches.

Update review of the acute porphyrias

Acute porphyrias are rare inherited disorders due to deficiencies of haem synthesis enzymes. To date, all UK cases have been one of the three autosomal dominant forms, although penetrance is low and most gene carriers remain asymptomatic. Clinical presentation is typically with acute neurovisceral attacks characterised by severe abdominal pain, vomiting, tachycardia and hypertension. Severe attacks may be complicated by hyponatraemia, peripheral neuropathy sometimes causing paralysis, seizures and psychiatric features. Attacks are triggered by prescribed drugs, alcohol, hormonal changes, fasting or stress. The diagnosis is made by finding increased porphobilinogen excretion in a light-protected random urine sample. Management includes administration of intravenous human haemin and supportive treatment with non-porphyrinogenic drugs. A few patients develop recurrent attacks, a chronic illness requiring specialist management. Late complications include chronic pain, hepatocellular carcinoma, chronic renal failure and hypertension. In the UK, the National Acute Porphyria Service provides clinical advice and supplies haemin when indicated.

An update of clinical management of acute intermittent porphyria

Acute intermittent porphyria (AIP) is due to a deficiency of the third enzyme, the hydroxymethylbilane synthase, in heme biosynthesis. It manifests with occasional neuropsychiatric crises associated with overproduction of porphyrin precursors, aminolevulinic acid and porphobilinogen. The clinical criteria of an acute attack include the paroxysmal nature and various combinations of symptoms, such as abdominal pain, autonomic dysfunction, hyponatremia, muscle weakness, or mental symptoms, in the absence of other obvious causes. Intensive abdominal pain without peritoneal signs, acute peripheral neuropathy, and encephalopathy usually with seizures or psychosis are the key symptoms indicating possible acute porphyria. More than fivefold elevation of urinary porphobilinogen excretion together with typical symptoms of an acute attack is sufficient to start a treatment. Currently, the prognosis of the patients with AIP is good, but physicians should be aware of a potentially fatal outcome of the disease. Mutation screening and identification of type of acute porphyria can be done at the quiescent phase of the disease. The management of patients with AIP include following strategies: A, during an acute attack: 1) treatment with heme preparations, if an acute attack is severe or moderate; 2) symptomatic treatment of autonomic dysfunctions, polyneuropathy and encephalopathy; 3) exclusion of precipitating factors; and 4) adequate nutrition and fluid therapy. B, during remission: 1) exclusion of precipitating factors (education of patients and family doctors), 2) information about on-line drug lists, and 3) mutation screening for family members and education about precipitating factors in mutation-positive family members. C, management of patients with recurrent attacks: 1) evaluation of the lifestyle, 2) evaluation of hormonal therapy in women, 3) prophylactic heme therapy, and 4) liver transplantation in patients with severe recurrent attacks. D, follow-up of the AIP patients for long-term complications: chronic hypertension, chronic kidney insufficiency, chronic pain syndrome, and hepatocellular carcinoma.

Are delta-aminolevulinate dehydratase inhibition and metal concentrations additional factors for the age-related cognitive decline?

Aging is often accompanied by cognitive impairments and influenced by oxidative status and chemical imbalances. Thus, this study was conducted to examine whether age-related cognitive deficit is associated with oxidative damage, especially with inhibition of the enzyme delta-aminolevulinate dehydratase (ALA-D), as well as to verify the influence of some metals in the enzyme activity and cognitive performance. Blood ALA-D activity, essential (Fe, Zn, Cu, Se) and non-essential metals (Pb, Cd, Hg, As, Cr, Ni, V) were measured in 50 elderly and 20 healthy young subjects. Cognitive function was assessed by tests from Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) battery and other. The elderly group presented decreased ALA-D activity compared to the young group. The index of ALA-D reactivation was similar to both study groups, but negatively associated with metals. The mean levels of essential metals were within the reference values, while the most toxic metals were above them in both groups. Cognitive function impairments were observed in elderly group and were associated with decreased ALA-D activity, with lower levels of Se and higher levels of toxic metals (Hg and V). Results suggest that the reduced ALA-D activity in elderly can be an additional factor involved in cognitive decline, since its inhibition throughout life could lead to accumulation of the neurotoxic compound ALA. Toxic metals were found to contribute to cognitive decline and also to influence ALA-D reactivation.

Urinary 5-aminolevulinic acid in lead-exposed children

Lead intoxication can interfere with haem synthesis and alter the concentration of haem precursors, such as the neurotoxin 5-aminolevulinic acid, in plasma and urine. The relationship between blood lead concentration (PbB), a biomarker of lead exposure, and 5-aminolevulinic acid concentration in urine (ALAU), a biomarker of the early biological effect of lead, was examined in lead-exposed children. ALAU was assayed by chemical derivatization and high performance liquid chromatography with fluorescence detection. The study subjects were 79 children with moderate to high lead exposure recruited from a lead-poisoning prevention clinic. Their urine had been previously analysed for creatinine (CR) concentration and the benzene metabolite trans,trans- muconic acid, and their blood had been analysed for lead. We found that ALAU was not correlated with PbB (Spearman r=0.088, p=0.44), but the ratio ALAU/CR was correlated with PbB (Spearman r=0.22, p=0.054). Creatinine and ALAU concentrations were higher in urine samples collected in the afternoon than those collected in the morning, a finding that is consistent with known diurnal variation. However the ratio ALAU/CR was not different in morning and afternoon urines, supporting the use of creatinine adjustment of ALAU analysis of spot urine samples. In view of the neurotoxic properties of ALA, future validation studies of biomarkers of lead exposure and effect in children should include ALAU or ALAU/CR as potential markers of lead effect.

ALA and its clinical impact, from bench to bedside

ALA-induced protoporphyrin IX (PpIX) is used for fluorescence diagnosis (ALA-FD) and for fluorescence-guided resection of both (pre)malignant and non-malignant diseases. ALA is also applied in photodynamic therapy (ALA-PDT) of superficial (pre)malignant lesions in dermatology, urology, neurosurgery, otorhinolaryngology, gynecology and gastroenterology. Today, ALA is approved as Levulan for actinic keratoses, the ALA-methyl ester Metvix for actinic keratoses and basal cell carcinoma, the ALA-hexyl ester Hexvix for the diagnosis of bladder cancer and Gliolan for malignant glioma. The use of ALA for PDT and FD was established around 25 years ago, with most of the fundamental knowledge gained at the "bench" and implemented at the "bedside" due to the diligence of a few researchers within the first 10 years of research. After 1993 ALA research was taken up by many groups. For patient treatment, several factors are relevant. Administered mainly in a topical or oral form, ALA penetrates tissue in a sub-optimal way, which is currently improved by special techniques and the use of ALA-esters. PpIX accumulation is elevated in many malignant tissues, several tissue abnormalities, and in mucosa. It is also found at elevated levels in macrophages, dendritic cells and activated lymphocytes. Following sufficient PpIX accumulation in the target cells, irradiation is carried out which may be accompanied by a burning sensation at the treatment site. Due to a saturation process of PpIX formation and rapid photobleaching during irradiation the risk of overtreatment is relatively low. Pharmacokinetical studies have demonstrated a low systemic photosensitivity and excretion of PpIX via natural routes.

Acute intermittent porphyria, Rasmussen encephalitis, or both?

A case of a young woman who suffers from refractory epilepsy in the form of Rasmussen encephalitis and acute intermittent porphyria is presented. The patient developed refractory partial seizures with progressive hemispheric atrophy in the first decade. Both her serum and cerebrospinal fluid contained significantly elevated levels of anti-GluR3B antibodies. Her serum also contained anti-NR2A antibodies (directed against the N-methyl-D-aspartate receptor). Seven years later, acute intermittent porphyria was diagnosed as she developed an acute episode of abdominal pain, dark urine, and hyponatremia. For several years, all attempts to discontinue porphyrinogenic antiepileptic drugs such as phenobarbital and valproate resulted in seizure worsening. During a major acute intermittent porphyria crisis, brain edema and coma developed, allowing the discontinuation of phenobarbital. On recovery, atrophy of the right hemisphere ensued. Several etiologic hypotheses are presented. Double insults, porphyria, and an autoimmune process are suggested for the development of Rasmussen encephalitis in this patient. The authors recommend testing for porphyria in cases of Rasmussen encephalitis and other intractable seizures.

Epilepsy and porphyria: new perspectives

Porphyria is a group of disorders caused by alterations in the enzymatic pathway involved in haem biosynthesis. The clinical picture consists of extraneurological and neurological manifestations, seizures being an important feature. The pathogenesis of seizures is probably related to metabolic imbalance such as hyponatremia and to the intrinsic epileptogenic role of some porphyrins. Many studies report that neural damage can follow a porphyric attack, suggesting that these lesions can be epileptogenic. Several reports also pointed out that porphyria can be precipitated by some antiepileptic drugs (AEDs). More recent AEDs appeared and need assessment in relation to porphyria. An educational program including a registry of patients with porphyria, an intensive study of family history and the genetic background may be useful to obtain better epidemiological data and a clearer understanding of pathogenesis. Application of neuroimaging may detect epileptogenic foci, helping to define the specific risk of seizures for each patient.

Plasma 5-aminolevulinic acid concentration and lead exposure in children

The relationship between concentration of 5-aminolevulinic acid in plasma (ALAP) and other biomarkers of lead exposure and effect was investigated in lead-exposed children. We measured ALAP by chemical derivatization and high-performance liquid chromatography with fluorescence detection. The study population consisted of 103 children: 78 from a referral clinic for children with lead poisoning and 25 from a general pediatric clinic. Blood lead concentration (PbB), age, and ALAP were higher in lead clinic subjects than in general clinic subjects. ALAP was significantly correlated with PbB (Spearman r=0.38, P=0.0007) and free erythrocyte protoporphyrin concentration (r=0.41, P=0.0002) in lead clinic subjects. PbB was a significant predictor of ALAP (P=0.0001) by multiple linear regression in all subjects. The average PbB in the 3- to 12-month period prior to blood collection correlated with ALAP to the same degree that current PbB correlated with ALAP. Possible associations between ALAP and adverse health outcomes, particularly neurobehavioral effects, should be investigated in children to assess the predictive value of ALAP for these endpoints.

Effects of delta-aminolaevulinic acid upon electrical activity of rat spinal cord in vivo

Bath applied delta-aminolaevulinic acid (ALA, 1-1000 microM), significantly depressed the frequency of spontaneous antidromic activity in the lumbar dorsal roots, and the amplitude of the monosynaptic component of the dorsal root-evoked ventral root reflex, in isolated rat spinal cord in a concentration-related manner. In contrast bath concentrations up to 1 mM ALA were found to produce no significant change in either the conducted afferent volley, nor field potentials recorded in the lumbar dorsal horn. These results indicate that the raised levels of ALA found in cerebrospinal fluid during porphyrias and lead poisoning may contribute to the neurological symptoms of these diseases.

The genetic effects of environmental lead

This article reviews the effects of lead on genetic systems in the context of lead's various other toxic effects and its abundance and distribution in the environment. Lead is perhaps the longest used and best recognized toxic environmental chemical, yet it continued be used recklessly until only very recently. Lead is thus a lesson in the limitations and strengths of science, human conscience and common sense. Lead has been tested and found to be capable of eliciting a positive response in an extraordinarily wide range of biological and biochemical tests; among them tests for enzyme inhibition, fidelity of DNA synthesis, mutation, chromosome aberrations, cancer and birth defects. It reacts or complexes with many biomolecules and adversely affects the reproductive, nervous, gastrointestinal, immune, renal, cardiovascular, skeletal, muscular and hematopoietic systems as well as developmental processes. It is likely that lead is a selective agent that continues to act on and influence the genetic structure and future evolution of exposed plant and animal populations.

Endogenous protoporphyrin IX, a clinically useful photosensitizer for photodynamic therapy

The tissue photosensitizer protoporphyrin IX (PpIX) is an immediate precursor of heme in the biosynthetic pathway for heme. In certain types of cells and tissues, the rate of synthesis of PpIX is determined by the rate of synthesis of 5-aminolevulinic acid (ALA), which in turn is regulated via a feedback control mechanism governed by the concentration of free heme. The presence of exogenous ALA bypasses the feedback control, and thus may induce the intracellular accumulation of photosensitizing concentrations of PpIX. However, this occurs only in certain types of cells and tissues. The resulting tissue-specific photosensitization provides a basis for using ALA-induced PpIX for photodynamic therapy. The topical application of ALA to certain malignant and non-malignant lesions of the skin can induce a clinically useful degree of lesion-specific photosensitization. Superficial basal cell carcinomas showed a complete response rate of approximately 79% following a single exposure to light. Recent preclinical studies in experimental animals and human volunteers indicate that ALA can induce a localized tissue-specific photosensitization if administered by intradermal injection. A generalized but still quite tissue-specific photosensitization may be induced if ALA is administered by either subcutaneous or intraperitoneal injection or by mouth. This opens the possibility of using ALA-induced PpIX to treat tumors that are too thick or that lie too deep to be accessible to either topical or locally injected ALA.

A comparative study of the effects of delta-aminolaevulinic acid and the GABAA agonist, muscimol, in rat jejunal preparations

Preparations of rat jejunum were tested for their responsiveness to the GABAA receptor agonist, muscimol, and to the haem precursor, delta-aminolaevulinic acid (ALA). Both muscimol (1.0-30 microM) and ALA (1.0 microM-3.0 mM) elicited a concentration-dependent increase in tone. Pretreatment with the GABAA antagonist, bicuculline (10(-5) M), blocked effects of muscimol at all concentrations tested and attenuated effects of 0.3 mM ALA. However, bicuculline enhanced responsiveness of the preparations to ALA at low concentrations (0.01-0.05 microM), as also did picrotoxin (10(-5) M), eliciting a significant increase of tone. The significance of these findings is discussed. This finding of pharmacological activity by ALA at concentrations comparable with its blood levels during acute attacks of intermittent porphyria provides support for the proposal that is may play a role in the aetiology of the gastrointestinal manifestations of this disease.

Pharmacological activities of delta-aminolaevulinic acid, protoporphyrin IX and haemin in isolated preparations of rabbit gastric fundus and jejunum

1. Pharmacological effects of delta-aminolaevulinic acid (ALA), protoporphyrin IX and haemin were examined in isolated preparations of rabbit jejunum and gastric fundus suspended in oxygenated Ringer-Locke solution at pH 7.0. 2. In jejunal preparations, delta-aminolaevulinic acid (3.0-4.5 mM), protoporphyrin IX (1.1-2.2 mM) and haemin (3.0-4.5 mM) dose-dependently reduced the amplitude of contractions and increased resting length. Pretreatment with prazosin (10(-7) M) inhibited effects produced by delta-aminolaevulinic acid (3 mM) and protoporphyrin IX (1.1 mM) but not those of haemin (3 mM). 3. In fundic preparations, dose-dependent contracture occurred in response to delta-aminolaevulinic acid (0.1-3.0 mM) protoporphyrin IX (0.1-2.2 mM) and haemin (0.6-6.3 mM). Effects qualitatively resembled those of noradrenaline (0.1-0.4 microM). Prazosin (10(-7) M) attenuated these effects, depressing the maximum response and causing a rightward shift of the concentration-response curves. 4. It is concluded that actions of delta-aminolaevulinic acid at alpha 1-adrenoceptor sites are unlikely to be related to the autonomic neuropathy of acute porphyria. Its in vitro effects occurred only at comparatively high concentrations and were mimicked by protoporphyrin IX and haemin. It is suggested that ALA is more likely to modify autonomic functions by an indirect action, since it is known at low dose levels to influence GABA-ergic functioning.

Pharmacological effects of haem biosynthetic intermediates in isolated intestinal preparations

Spontaneous contractile activity of isolated rabbit jejunal preparations bathed in oxygenated Ringer-Locke buffered to pH 7.0 was inhibited by haemin and by all haem biosynthetic intermediates tested, there being decreases in tone or amplitude of contractions. Effects were concentration-dependent. The minimal effective concentrations were 0.4 mM for porphobilinogen, 0.6 mM for protoporphyrin IX, 0.8 mM for haemin, 3.0 mM for delta-aminolaevulinic acid (ALA), 4.5 mM for coproporphyrin I, 3.0 mM for glycine and 6.0 mM for succinate. Inhibition was short-lasting, other than for protoporphyrin (2.3 mM) and haemin (3.0 mM). Leucine at concentrations up to 12 mM had no significant effect. Inhibitory effects of ALA were followed by contractions of increased amplitude; pretreatment of preparations with indomethacin (56 microM) prevented this enhancement of contractile activity. Tone in isolated preparations of human taenia coli bathed in oxygenated Ringer-Locke was decreased by ALA (1.5-6.0 mM). A significant increase of tone followed the initial inhibitory effect. The relevance of these findings to acute porphyria is discussed.

Effects of delta-aminolaevulinic acid on contractile activity in the isolated small intestine of the rabbit. Role of adrenergic receptors

The porphyrin precursor, delta-aminolaevulinic acid (ALA) at concentrations of 0.23-7.6 mM caused dose-dependent inhibition of spontaneous contractions in isolated preparations of rabbit small intestine, suspended in Ringer-Locke solution. Contractions which returned after inhibition from 3.8 and 7.6mM ALA showed increased amplitude and from 7.6 mM ALA a reduction in rate. Pretreatment with prazosin (10(-7) M) significantly reduced the duration of inhibition exerted by 3.8 and 7.6 mM ALA and also the amplitude of contractions returning after this inhibition. Pretreatment with yohimbine (10(-6) M) and propranolol (7 X 10(-6) M) had no significant effects. Blocking of the release of noradrenaline in preparations by incubation with 6-hydroxydopamine (10(-3) M) or guanethidine (1.5 X 10(-5) M) did not prevent the inhibitory effects of ALA. The alpha 1 agonist, cirazoline (10(-5) M), inhibited contractile activity. This effect was blocked by prazosin (10(-7) M). The alpha 2 agonist, guanoxabenz (10(-5) M) had no detectable effect, in the presence of prazosin, to block any residual alpha 1 actions. It is concluded that alpha 1 receptors mediate inhibitory effects in this preparation and that ALA appears to have direct effects upon these receptors.

The effect of delta-aminolaevulinic acid on the high affinity uptake of aspartic acid by rat brain synaptosomes

delta-Aminolaevulinic (delta-ALA) acid is an analogue of GABA, glutamate and aspartate. High affinity GABA uptake by synaptosomes is inhibited by delta-ALA in a competitive fashion at high concentrations (greater than 0.5 mM). Glutamate uptake is inhibited in a non-competitive fashion at all delta-ALA concentrations (0.05-2.0 mM). High affinity aspartate uptake is inhibited in a non-competitive fashion at high concentration (greater than 1.0 mM) but exhibits a curve which resembles that for the inhibition of GABA uptake. The different interactions between delta-ALA, glutamate and aspartate may be evidence for a separate transport system for aspartate.