Increased plasma tryptophan in HIV-infected patients treated with pharmacologic doses of nicotinamide

Accelerated cognitive aging in chronically infected HIV-1 positive individuals despite effective long-term antiretroviral therapy

People living with HIV (PLHIV) are known to be at a higher risk of developing an array of aging-related diseases despite well-adhered combined antiretroviral therapy (cART). The present study aimed to investigate the impact of chronic HIV infection on neurocognitive function in virally suppressed PLHIV. We enrolled HIV-positive individuals randomly from an ART Center in Chennai, South India. A similar number of HIV-uninfected individuals matched for age and gender with the HIV-infected individuals served as controls. All individuals provided a detailed clinical history and underwent neuropsychological assessment using the International HIV Dementia Scale (IHDS). Plasma proteome analysis was performed using the Proximity extension assay (PEA) with the Olink® neuroexploratory panel, and untargeted metabolomics was performed using Ultra-High-Performance Liquid Chromatography/Mass Spectrometry/Mass Spectrometry. Despite a median duration of 9 years on first-line cART and suppressed viremia, a significant proportion of PLHIV registered significant levels of asymptomatic neurocognitive impairment, with 71% of these individuals scoring ≤ 10 in the IHDS test. We also observed significant alterations in a number of proteins and metabolites that are known to be associated with neuroinflammation, neurodegeneration, cognitive impairment, and gastrointestinal cancers, in the PLHIV group. Thus the study provides clinical as well as laboratory evidence to substantiate the presence of asymptomatic neurocognitive impairment in a large proportion of PLHIV, despite adequate cART and undetectable viremia, thereby supporting the view that HIV infection potentiates the risk for accelerated and accentuated neurological aging. This observation highlights the need to devise and implement appropriate intervention strategies for better long term management of HIV-infected persons.

Gut microbiota-derived vitamins - underrated powers of a multipotent ally in psychiatric health and disease

Despite the well-established roles of B-vitamins and their deficiencies in health and disease, there is growing evidence indicating a key role of those nutrients in functions of the central nervous system and in psychopathology. Clinical data indicate the substantial role of B-vitamins in various psychiatric disorders, including major depression, bipolar disorder, schizophrenia, autism, and dementia, including Alzheimer's and Parkinson's diseases. As enzymatic cofactors, B-vitamins are involved in many physiological processes such as the metabolism of glucose, fatty acids and amino acids, metabolism of tryptophan in the kynurenine pathway, homocysteine metabolism, synthesis and metabolism of various neurotransmitters and neurohormones including serotonin, dopamine, adrenaline, acetylcholine, GABA, glutamate, D-serine, glycine, histamine and melatonin. Those vitamins are highly involved in brain energetic metabolism and respiration at the cellular level. They have a broad range of anti-inflammatory, immunomodulatory, antioxidant and neuroprotective properties. Furthermore, some of those vitamins are involved in the regulation of permeability of the intestinal and blood-brain barriers. Despite the fact that a substantial amount of the above vitamins is acquired from various dietary sources, deficiencies are not uncommon, and it is estimated that micronutrient deficiencies affect about two billion people worldwide. The majority of gut-resident microbes and the broad range of bacteria available in fermented food, express genetic machinery enabling the synthesis and metabolism of B-vitamins and, consequently, intestinal microbiota and fermented food rich in probiotic bacteria are essential sources of B-vitamins for humans. All in all, there is growing evidence that intestinal bacteria-derived vitamins play a significant role in physiology and that dysregulation of the "microbiota-vitamins frontier" is related to various disorders. In this review, we will discuss the role of vitamins in mental health and explore the perspectives and potential of how gut microbiota-derived vitamins could contribute to mental health and psychiatric treatment.

Impact of extended-release niacin on immune activation in HIV-infected immunological non-responders on effective antiretroviral therapy

BACKGROUND

Background: Tryptophan (Trp) catabolism into immunosuppressive kynurenine (Kyn) is involved in immune dysregulation during HIV infection. Niacin (vitamin B3) could control the excess of tryptophan depletion and represents a potential strategy to improve immune functions and CD4 count recovery in immunological non-responder HIV-infected individuals on antiretroviral therapy (ART).

METHODS

Methods: In the CTN PT006 phase 2 pilot randomized trial, 20 adults on ART with CD4 ≤ 350 cells/µl, despite an undetectable viral load (VL) for at least 3 months, received 2000 mg of extended-release (ER)-niacin orally once daily for 24 weeks. Side effects, VL, CD4/CD8 counts, lipid profile, T-cell activation and senescence, Tregs and Th17 cell frequencies, Kyn/Trp ratio, and levels of IL-6, IP-10, sST2, I-FABP, and LBP were assessed following ER-niacin treatment.

RESULTS

Results: Thirteen participants completed the study. Treatment was interrupted in 4 patients due to loss of follow-up or personal reasons and 3 patients were discontinued due to comorbidity risks. All participants maintained a VL < 40 copies/ml, while ER-niacin did not affect CD4 and CD8 cell counts. Plasma levels of triglycerides, total, and LDL cholesterol significantly decreased, following ER-niacin treatment. ER-niacin also diminished Kyn plasma levels and slightly decreased CD4 T-cell activation. However, no improvement in CD8 subsets, Kyn/Trp ratio, Th17/Treg balance, and plasma inflammatory markers was observed.

CONCLUSIONS

Conclusions: Although ER-niacin combined with ART was well-tolerated among immune non-responders and decreased plasma lipids, it did not improve systemic inflammation, Kyn/Trp ratio, and CD4 cell recovery. Overall, ER-niacin was not effective to overcome chronic inflammation in PLWH.

Indoleamine 2, 3-Dioxygenase-Mediated Tryptophan Catabolism: A Leading Star or Supporting Act in the Tuberculosis and HIV Pas-de-Deux?

Progression from latency to active Tuberculosis (TB) disease is mediated by incompletely understood host immune factors. The definitive characteristic of progressive human immunodeficiency virus (HIV) disease is a severe loss in number and function of T lymphocytes. Among the many possible mediators of T lymphocyte loss and ineffective function is the activity of the immune-modulatory enzyme indoleamine 2,3-dioxygenase (IDO). IDO is the rate-limiting enzyme converting tryptophan to kynurenine. IDO activity was initially recognized to mediate tolerance at the foeto-maternal interface. Recently, IDO activity has also been noted to play a critical role in immune tolerance to pathogens. Studies of host immune and metabolic mediators have found IDO activity significantly elevated in HIV and TB disease. In this review, we explore the link between IDO-mediated tryptophan catabolism and the presence of active TB disease in HIV-infected patients. We draw attention to increased IDO activity as a key factor marking the progression from latent to active TB disease in HIV-infected patients.

Pellagra in isoniazid preventive and antiretroviral therapy

Pellagra is caused by cellular deficiency of niacin or its precursor amino acid, tryptophan. Isoniazid preventive therapy (IPT) is the administration of isoniazid (INH) to latent tuberculosis (TB) infection affected people preventing advancement to active TB disease. Although potentially life-saving for human immunodeficiency virus (HIV)-infected people with no active TB, IPT is arguably a possible player in pellagra in addition to well-known malnourishment determinants particularly in developing nations where diagnosis is often overlooked or delayed.

A case study examines clinical presentation and possible causes of pellagra, in HIV + patient on isoniazid prophylaxis. The 30 year old female on routine antiretroviral therapy presented with diarrhea, abdominal discomfort, painful swallowing, and epigastric pain, facial rash spread on the forehead, nose, cheeks and the chin, upper and lower limbs. Withdrawal of isoniazid, administration of nicotinamide and niacin supplements showed clinical improvement in four weeks. Decreased serum tryptophan in persons living with HIV (PLHIV) under IPT and lack of minimum dietary proteins threshold would be pointers to isoniazid induced pellagra risk. Appropriate dietary intake and counseling ought to be emphasized among PLHIV. Tryptophan and nicotinamide serum levels should be part of baseline investigations in PLHIV starting IPT and where feasible clinically, niacin/nicotinamide supplementation be adopted.

Niacin

Nicotinic acid and nicotinamide, collectively referred to as niacin, are nutritional precursors of the bioactive molecules nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). NAD and NADP are important cofactors for most cellular redox reactions, and as such are essential to maintain cellular metabolism and respiration. NAD also serves as a cosubstrate for a large number of ADP-ribosylation enzymes with varied functions. Among the NAD-consuming enzymes identified to date are important genetic and epigenetic regulators, e.g., poly(ADP-ribose)polymerases and sirtuins. There is rapidly growing knowledge of the close connection between dietary niacin intake, NAD(P) availability, and the activity of NAD(P)-dependent epigenetic regulator enzymes. It points to an exciting role of dietary niacin intake as a central regulator of physiological processes, e.g., maintenance of genetic stability, and of epigenetic control mechanisms modulating metabolism and aging. Insight into the role of niacin and various NAD-related diseases ranging from cancer, aging, and metabolic diseases to cardiovascular problems has shifted our view of niacin as a vitamin to current views that explore its potential as a therapeutic.

Photosensitive disorders in HIV

Photosensitive disorders are common, affecting up to 5% of HIV-positive patients. HIV itself induces photosensitivity but photoaggravated drug reactions, porphyria cutanea tarda and nutritional disorders such as pellagra are also more common in patients with HIV. In South Africa, actinic lichenoid leukomelanoderma of HIV is a unique photosensitive disorder which is associated with advanced HIV. It is important to be able to recognise these conditions and withdraw photosensitising medications wherever possible.

Tryptophan depletion in context of the inflammatory and general nutritional status of a low-income South African HIV-infected population

BACKGROUND

The essential amino acid tryptophan cannot be synthesised in the body and must be acquired through dietary intake. Oxidation of tryptophan, due to immune induction of the enzyme indoleamine 2,3-dioxygenase (IDO), is considered to be the main cause of tryptophan depletion in HIV infection and AIDS. We examined plasma tryptophan levels in a low-income sub-Saharan HIV-infected population and compared it to that of developed countries. Tryptophan levels were further examined in context of the general nutritional and inflammatory status.

METHODS

This cross-sectional study included 105 HIV-positive patients recruited from the Kalafong Hospital in Pretoria, South Africa, and 60 HIV-negative controls.

RESULTS

Patient tryptophan levels were in general markedly lower than those reported for developed countries. In contrast to reports from developed countries that showed tryptophan levels on average to be 18.8 % lower than their control values, tryptophan levels in our study were 44.1 % lower than our controls (24.4 ± 4.1 vs. 43.6 ± 11.9 μmol/l; p < 0.001). Tryptophan levels correlated with both CD4 counts (r = 0.341; p = 0.004) and with pro-inflammatory activity as indicated by neopterin levels (r = -0.399; p = 0.0001). Nutritional indicators such as albumin and haemoglobin correlated positively with tryptophan and negatively with the pro-inflammatory indicators neopterin, interleukin 6 and C-reactive protein. The most probable causes of the lower tryptophan levels seen in our population are food insecurity and higher levels of inflammatory activity.

CONCLUSIONS

We contend that inflammation-induced tryptophan depletion forms part of a much wider effect of pro-inflammatory activity on the nutritional profile of HIV-infected patients.

The kynurenine pathway activities in a sub-Saharan HIV/AIDS population

BACKGROUND

Tryptophan is an essential amino acid for the synthesis of proteins and important metabolites such as serotonin, melatonin, tryptamine and niacin. After protein synthesis, more than 90 % of tryptophan catabolism occurs along the kynurenine pathway. The inflammation-inducible enzyme indoleamine 2,3 dioxygenase (IDO) is responsible for the first rate-limiting step in the kynurenine pathway, i.e., oxidation of tryptophan to kynurenine. Excessive IDO activity in conditions such as HIV/AIDS may lead to tryptophan depletion and accumulation of metabolites downstream from kynurenine. Little is known about the kynurenine pathway of HIV/AIDS patients in sub-Saharan regions. This study, in a low income sub-Saharan HIV/AIDS population, examined the effects of activities in the kynurenine pathway on plasma levels of tryptophan, kynurenine and the neurotoxin quinolinic acid, and on de novo synthesis of nicotinamide.

METHODS

Plasma samples were obtained from a cohort of 105 HIV patients and 60 controls. Kynurenine pathway metabolites were analysed using gas chromatography - mass spectrometry. ELISA and flow cytometry were used to assess plasma inflammatory markers.

RESULTS

IDO activity, depletion of tryptophan, as well as accumulation of kynurenine and the neurotoxin quinolinic acid, were not only significantly greater in the patients than in the controls, but also markedly greater than in HIV/AIDS patients from developed countries. Tryptophan levels were 12.3 % higher, kynurenine levels 16.2 % lower, quinolinic acid levels 43.2 % lower and nicotinamide levels 27,2 % lower in patients on antiretroviral treatment than in antiretroviral-naïve patients. Patients' kynurenine pathway metabolites correlated with the levels of inflammatory markers, including that of the major IDO-inducer, interferon-gamma. Indications are that the rate of de novo synthesis of nicotinamide in the kynurenine pathway correlates with increases in quinolinic acid levels up to a point where saturation of the enzyme quinolinate phosphoribosyl transferase occurs.

CONCLUSIONS

Higher levels of inflammatory activity in this low income sub-Saharan HIV/AIDS population than in patients from developed countries lead to greater tryptophan depletion and greater accumulation of metabolites downstream from tryptophan with quinolinic acid levels often reaching levels associated with the development of HIV/AIDS-associated neurocognitive dysfunction. De novo synthesis of nicotinamide from quinolinic acid contributes to the maintenance of nicotinamide, and by implication NAD levels, in HIV/AIDS patients from low income populations. Antiretroviral treatment partially corrects disturbances in the kynurenine pathway.

Disturbed Amino Acid Metabolism in HIV: Association with Neuropsychiatric Symptoms

Blood levels of the amino acid phenylalanine, as well as of the tryptophan breakdown product kynurenine, are found to be elevated in human immunodeficiency virus type 1 (HIV-1)-infected patients. Both essential amino acids, tryptophan and phenylalanine, are important precursor molecules for neurotransmitter biosynthesis. Thus, dysregulated amino acid metabolism may be related to disease-associated neuropsychiatric symptoms, such as development of depression, fatigue, and cognitive impairment. Increased phenylalanine/tyrosine and kynurenine/tryptophan ratios are associated with immune activation in patients with HIV-1 infection and decrease upon effective antiretroviral therapy. Recent large-scale metabolic studies have confirmed the crucial involvement of tryptophan and phenylalanine metabolism in HIV-associated disease. Herein, we summarize the current status of the role of tryptophan and phenylalanine metabolism in HIV disease and discuss how inflammatory stress-associated dysregulation of amino acid metabolism may be part of the pathophysiology of common HIV-associated neuropsychiatric conditions.

Antidepressants may lead to a decrease in niacin and NAD in patients with poor dietary intake

The term niacin is the generic name for the two compounds nicotinic acid and nicotinamide, the major dietary precursors for two important coenzymes, nicotinamide adenine dinucleotide (NAD) and its phosphorylated form, NADP. Niacin is important for the maintenance of cellular integrity and energy production and is involved in more than 500 intracellular reactions. Deficiencies of niacin may contribute to neuropsychiatric and neurodegenerative disorders. Patients who develop nutritional deficiencies as a result of poor dietary intake, especially inadequate intake of proteins and vitamins, could potentially suffer from niacin deficiency and NAD depletion. However, de novo synthesis of niacin and NAD in the kynurenine pathway of tryptophan metabolism may compensate for impaired dietary intake. The rate of synthesis of NAD and niacin from tryptophan oxidation depends on the induction of the enzyme indoleamine 2,3-dioxygenase (IDO) by pro-inflammatory cytokines such as interferon-gamma. Niacin synthesis is not limited by a decrease in tryptophan and excessive IDO activity may therefore lead to a decline in tryptophan levels. Antidepressants have an anti-inflammatory effect, including reduction of interferon-gamma and therefore inhibition of IDO, the rate-limiting enzyme of the kynurenine pathway. In theory, this could account for increased serotonin as more tryptophan becomes available for serotonin synthesis. However, the downside may be that less NAD and niacin are synthesised downstream, which could exacerbate common psychiatric problems. It is our hypothesis that patients with poor dietary intake, who are treated with antidepressants, are at risk of developing niacin/NAD deficiency with possible development of associated neuropsychiatric symptoms. We therefore propose that niacin supplementation be considered in patients with inadequate diets who are treated with antidepressants. We believe that if this does not happen, a subclinical niacin deficiency may result, which would be difficult to detect as it would cause the same symptoms of the original illness (e.g. depression). Niacin deficiency should be considered and ruled out in all patients with treatment-resistant depression, who have a poor response to antidepressants. This is potentially a cost-effective and easy intervention, which could be examined in a randomized controlled trial.

The role of extended-release niacin on immune activation and neurocognition in HIV-infected patients treated with antiretroviral therapy - CTN PT006: study protocol for a randomized controlled trial

BACKGROUND

Approximately 30% of HIV-1-infected patients receiving antiretroviral therapy who achieve virologic control have unsatisfactory immune reconstitution, with CD4+ T-cell counts persistently below 350 cells/μL. These patients are at elevated risk for clinical progression to AIDS and non-AIDS events. CD4+ T-cell depletion following infection and persistent immune activation can partially explain this low CD4+ T-cell recovery. Recent data suggest a link between the tryptophan oxidation pathway, immune activation and HIV disease progression based on overstimulation of the tryptophan oxidation pathway by HIV antigens and by interferon-gamma. This overstimulation reduces levels of circulating tryptophan, resulting in inflammation which has been implicated in the development of neurocognitive dysfunction. Niacin (vitamin B3) is able to control the excess tryptophan oxidation, correcting tryptophan depletion, and therefore represents an interesting strategy to improve CD4 recovery.We aim to design a crossover proof-of-concept study to assess supplementation with an extended-release form of niacin (Niaspan FCT™) in combination with antiretroviral therapy, compared to antiretroviral therapy alone, on T-cell immune activation as defined by changes in the percentage of CD8+ CD38+ HLA-DR+ T-cells.

METHODS/DESIGN

This randomized, open-label, interventional crossover study with an immediate versus deferred use of Niaspan FCT for 24 weeks will assess its ability to reduce immune activation and thus increase CD4 recovery in 20 HIV-infected individuals with suboptimal immune responses despite sustained virologic suppression. A substudy evaluating neurocognitive function will also be conducted.

DISCUSSION

This randomized trial will provide an opportunity to evaluate the potential benefit of oral extended-release niacin, a drug that can indirectly increase tryptophan, to reduce immune activation and in turn increase CD4+ T-cell recovery. The study will also allow for the evaluation of the impact of Niaspan FCT on neurocognitive function in HIV-infected individuals with suboptimal immune responses despite sustained virologic suppression.

TRIAL REGISTRATION

This study was registered with ClinicalTrials.gov on 17 December 2013 (registration number: NCT02018965).

HIV infection and drugs of abuse: role of acute phase proteins

Background

HIV infection and drugs of abuse such as methamphetamine (METH), cocaine, and alcohol use have been identified as risk factors for triggering inflammation. Acute phase proteins such as C-reactive protein (CRP) and serum amyloid A (SAA) are the biomarkers of inflammation. Hence, the interactive effect of drugs of abuse with acute phase proteins in HIV-positive subjects was investigated.

Methods

Plasma samples were utilized from 75 subjects with METH use, cocaine use, alcohol use, and HIV-positive alone and HIV-positive METH, cocaine, and alcohol users, and age-matched control subjects. The plasma CRP and SAA levels were measured by ELISA and western blot respectively and the CD4 counts were also measured.

Results

Observed results indicated that the CRP and SAA levels in HIV-positive subjects who are METH, cocaine and alcohol users were significantly higher when compared with either drugs of abuse or HIV-positive alone. The CD4 counts were also dramatically reduced in HIV-positive with drugs of abuse subjects compared with only HIV-positive subjects.

Conclusions

These results suggest that, in HIV-positive subjects, drugs of abuse increase the levels of CRP and SAA, which may impact on the HIV infection and disease progression.

Kynurenine Pathway Pathologies: do Nicotinamide and Other Pathway Co-Factors have a Therapeutic Role in Reduction of Symptom Severity, Including Chronic Fatigue Syndrome (CFS) and Fibromyalgia (FM)

The definition of dual tryptophan pathways has increased the understanding of the mind-body, body-mind dichotomy. The serotonergic pathway highlights the primary (endogenous) psychiatric disorders. The up-regulation of the kynurenine pathway by physical illnesses can cause neuropathic and immunological disorders1 associated with secondary neuropsychiatric symptoms.

Tryptophan and nicotinamide deficiencies fall within the protein energy malnutrition (PEM) spectrum. They can arise if the kynurenine pathway is stressed by primary or secondary inflammatory conditions and the consequent imbalance of available catabolic/anabolic substrates may adversely influence convalescent phase efficiency. The replacement of depleted or reduced NAD+ levels and other cofactors can perhaps improve the clinical management of these disorders.

Chronic fatigue syndrome (CFS) and fibromyalgia (FM) appear to meet the criteria of a tryptophan-kynurenine pathway disorder with potential neuroimmunological sequelae. Aspects of some of the putative precipitating factors have been previously outlined.2,3 An analysis of the areas of metabolic dysfunction will focus on future directions for research and management.

Persistent infectious diseases say - IDO. Role of indoleamine-2,3-dioxygenase in disease pathogenesis and implications for therapy

Indoleamine-2,3-dioxygenase (IDO) is an enzyme that catabolises tryptophan - an essential amino acid critical for T cell proliferation. Initially recognized as a first line of host defense against infectious pathogens, IDO has been subsequently identified as an important immune-regulator inhibiting T-cell responses and promoting immune tolerance. Research over the past few years has demonstrated a crucial role for IDO in the pathogenesis of persistent infections that place an enormous burden on public health. In this review, we summarize current knowledge about IDO's role in causing pathogen persistence and progression to clinical disease. We conclude with a perspective on the potential benefits and risks of therapeutic IDO manipulation.

Insights into therapy: tryptophan oxidation and HIV infection

New data from Favre and colleagues strengthen the link between activation of the tryptophan oxidation (TOx) pathway--via the indoleamine 2,3-dioxygenase enzymes IDO1 and IDO2--and chronic inflammation in progressive HIV disease. It can now be appreciated that a pathogenic TOx activation cycle exists in HIV. TOx regulation is a therapeutic target for other diseases, such as cancer and autoimmune disorders. Here TOx control is examined with an eye to eventual therapeutic intervention in HIV disease.

The oxidative stress-induced niacin sink (OSINS) model for HIV pathogenesis

Although several specific micronutrient deficiencies are associated with disease progression and increased mortality risk in HIV/AIDS, and even a simple multivitamin/mineral supplement can prolong survival, this is typically viewed merely as nutritional support of the immune system, and only necessary if there are deficiencies to be rectified. However, the reality is more complex. Several striking nutrient-related metabolic abnormalities have been consistently documented in HIV infection. One is chronic oxidative stress, including a drastic depletion of cysteine from the glutathione pool, and a progressive decline of serum selenium that is correlated with disease progression and mortality. Another is decreased blood levels of tryptophan, with an associated intracellular niacin deficiency. Tryptophan depletion or "deletion" by induction of indoleamine-2,3-dioxygenase (IDO), the first step in oxidative tryptophan metabolism, is a known mechanism for immune suppression that is of critical importance in cancer and pregnancy, and, potentially, in HIV/AIDS. Existing evidence supports the hypothesis that these nutrient-related metabolic abnormalities in HIV infection regarding antioxidants, selenium, sulfur, tryptophan and niacin are interrelated, because HIV-associated oxidative stress can induce niacin/NAD+ depletion via activation of poly(ADP-ribose) polymerase (PARP), which could lead to tryptophan oxidation for compensatory de novo niacin synthesis, thereby contributing to immune tolerance and T-cell loss via tryptophan deletion and PARP-induced cell death. This "oxidative stress-induced niacin sink" (OSINS) model provides a mechanism whereby the oxidative stress associated with HIV infection can contribute to immunosuppression via tryptophan deletion. This model is directly supported by evidence that antioxidants can counteract indoleamine-2,3-dioxygenase (IDO), providing the critical link between oxidative stress and tryptophan metabolism proposed here. The OSINS model can be used to guide the design of nutraceutical regimens that can effectively complement antiretroviral therapy for HIV/AIDS.

Kynurenine pathway metabolites in humans: disease and healthy States

Tryptophan is an essential amino acid that can be metabolised through different pathways, a major route being the kynurenine pathway. The first enzyme of the pathway, indoleamine-2,3-dioxygenase, is strongly stimulated by inflammatory molecules, particularly interferon gamma. Thus, the kynurenine pathway is often systematically up-regulated when the immune response is activated. The biological significance is that 1) the depletion of tryptophan and generation of kynurenines play a key modulatory role in the immune response; and 2) some of the kynurenines, such as quinolinic acid, 3-hydroxykynurenine and kynurenic acid, are neuroactive. The kynurenine pathway has been demonstrated to be involved in many diseases and disorders, including Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, AIDS dementia complex, malaria, cancer, depression and schizophrenia, where imbalances in tryptophan and kynurenines have been found. This review compiles most of these studies and provides an overview of how the kynurenine pathway might be contributing to disease development, and the concentrations of tryptophan and kynurenines in the serum, cerebrospinal fluid and brain tissues in control and patient subjects.

Niacin nutritional status in HIV type 1-positive children: preliminary data

OBJECTIVE

HIV infection induces a state of pellagra in cell culture models. This study compared the nutritional status and the 24-hour urine excretion of N-methylnicotinamide between HIV-positive children and HIV-negative children who were or were not born of mothers with HIV-1 infection.

PATIENTS AND METHODS

Forty patients were included in the study: HIV-positive children (group 1; n = 20), HIV-negative children born to infected mothers (group 2; n = 10), and HIV-negative control children (group 3; n = 10). Usual dietary intake was assessed by a semiquantitative food-frequency questionnaire. Weight and height were assessed and compared with the reference data of the U.S. National Center for Health Statistics/Centers for Disease Control and Prevention. For the estimation of fat-free mass and total body water, bioelectrical impedance technique was used. N-methylnicotinamide was measured by a modified method of high-performance liquid chromatography.

RESULTS

Groups were matched in relation to age, sex, percentage of malnutrition, anthropometric measures, and body composition. Daily niacin intake did not differ statistically across groups (group 1 = 18.0 +/- 11.4 mg/day; group 2 = 18.9 +/- 8.0 mg/day; group 3 = 14.2 +/- 5.2 mg/day), nor did intake of tryptophan, vitamin B6, and zinc. The values of urinary niacin per gram of creatinine were similar and adequate across the groups (group 1 = 4.68 [0.75-14.9]; group 2 = 3.74 [1.13-5.69]; group 3 = 3.85 [1.80-8.19]).

CONCLUSIONS

HIV-positive children excreted the same amount of N-methylnicotinamide in urine as did the control children. These findings may be attributed to similarities in nutritional status, adequate intestinal absorption (no children experienced diarrhea) and stable clinical condition.

Niacin metabolite excretion in alcoholic pellagra and AIDS patients with and without diarrhea

OBJECTIVE

Malnourished patients with the acquired immunodeficiency syndrome (AIDS) can develop pellagra-like manifestations such as dermatitis, diarrhea, and dementia; therefore, we tested the hypothesis that patients with AIDS and diarrhea would have niacin depletion. This study compared 24-h urine excretion of N1-methyl-nicotinamide (N1MN) among patients with pellagra and patients with AIDS who did and did not have diarrhea.

METHODS

Three groups were studied: G1 (patients with AIDS and diarrhea, n = 5); G2 (patients with AIDS and no diarrhea, n = 7), and G3 (patients with alcoholic pellagra and without the human immunodeficiency virus, n = 8). Diarrhea was defined as the production of at least three liquid stools per day over 3 to 5 d. Studies included mucosal intestinal biopsy, malabsorption tests, detection of parasites in stool, and serum albumin measurements. Semiquantitative food-frequency questionnaire, anthropometry, and daily urinary N1MN excretion were also determined. Groups were matched in relation to age, sex, presence of parasites in stool, and intestinal absorption results.

RESULTS

G1 had normal intestinal examination by light microscopy and no parasites in stools. G2 group showed lower levels of serum albumin (2.6 +/- 0.3 g/dL) when compared with G1 (3.4 +/- 0.3 g/dL) and G3 (3.1 +/- 0.7 g/dL). Except for patients with pellagra, groups met their energy requirements. Patients in G3 (0.013, 0.01-0.081 mg/dL) and G1 (0.062, 0.001-0.33 mg/dL) excreted smaller amounts of N1MN in urine than did those in G2 (0.63, 0.02-2.9 mg/dL).

CONCLUSIONS

Patients with AIDS and diarrhea excreted less N1MN in urine than did those without diarrhea. These patients may have an impaired niacin nutritional status, possibly associated with increased metabolic needs.

Potential role for nonesterified fatty acids in β-adrenoceptor-induced increases in brain tryptophan

We tested the hypothesis that beta2- and beta3-adrenergic receptor-mediated increases in brain tryptophan are due to the liberation of fatty acids, which in turn displace tryptophan from its albumin-binding site and thus facilitate its entry into the brain. Male CD-1 mice were injected with subtype-selective beta-adrenergic agonists 1h before brain samples were collected for analysis of tryptophan content by HPLC with electrochemical detection, and blood samples were collected for analysis of total and free tryptophan and nonesterified fatty acid (NEFA) concentrations. The beta2-selective agonist, clenbuterol (0.1 mg/kg), increased concentrations of tryptophan in all brain regions studied and decreased plasma total tryptophan, but had no effect on plasma free tryptophan or NEFAs. The beta3-selective agonists, BRL 37344 (0.2 mg/kg) or CL 316243 (0.01 mg/kg), increased brain tryptophan, plasma NEFAs and free tryptophan. Pretreatment with nicotinic acid (500 mg/kg), an inhibitor of lipolysis, almost completely prevented the increase in plasma free tryptophan and NEFAs, and attenuated the increase in brain tryptophan induced by CL 316243. These results suggest that beta2- and beta3-adrenergic agonists increase brain tryptophan by a mechanism other than the liberation of NEFAs. Nonetheless, beta3-adrenergic agonists appear to increase brain tryptophan by a mechanism that may depend partially on elevations of plasma NEFAs.

Pellagra: dermatitis, dementia, and diarrhea

Pellagra defines systemic disease as resulting from a marked cellular deficiency of niacin. It is characterized by 4 "D's": diarrhea, dermatitis, dementia, and death. Diagnosis of pellagra is difficult in the absence of the skin lesions, and is often facilitated by the presence of characteristic ones. The dermatitis begins as an erythema. Acute pellagra resembles sunburn in its first stages, but tanning occurs more slowly than typically in sunburn. Exacerbation follows re-exposure to sunlight. In this work we review the findings of this once mysterious disorder, one that still challenges clinicians world-wide.

Tryptophan depletion and HIV infection: a metabolic link to pathogenesis

HIV-1-infected patients have low circulating tryptophan concentrations despite evidence of adequate dietary intake of this essential amino acid. A chronic increase in inducible tryptophan oxidation is the basis of HIV-1-associated tryptophan depletion. This metabolic process results in the irretrievable loss of tryptophan molecules from the available pool. Such sustained disruption of normal tryptophan metabolism over time disturbs the many metabolic processes involving this amino acid, and has been implicated in some features of AIDS pathogenesis. Normal T-cell function is adversely affected by tryptophan depletion, but the extent of the effect in HIV-1-infected patients is still unclear. Attempting to directly supplement tryptophan is not advised given the potential increase in circulating concentrations of neurotoxic intermediates. Although only preliminary data are available, evidence suggests that antiretroviral and nicotinamide treatments can boost plasma tryptophan concentrations in HIV-1-infected patients and impact the secondary effects of tryptophan depletion. Additional study of this metabolism could lead to improved treatment strategies for patients with HIV infection. In this review I focus on the potential links between disturbed tryptophan metabolism and pathogenesis.

Nicotinamide: an oral antimicrobial agent with activity against both Mycobacterium tuberculosis and human immunodeficiency virus

Coinfection with Mycobacterium tuberculosis and human immunodeficiency virus (HIV) is responsible for one-third of all deaths due to acquired immunodeficiency syndrome. More than 99% of cases of HIV-M. tuberculosis coinfection occur in the developing world, where limited resources add urgency to the search for effective and affordable therapies. Although antimicrobial agents against each of these infections are available, single agents that have activity against both M. tuberculosis and HIV are uncommon. The activity of nicotinamide has been evaluated in 2 different eras: in anti-M. tuberculosis studies performed during 1945-1961 and in anti-HIV studies performed from 1991 to the present. This review brings together these 2 bodies of inquiry and raises the possibility that, with more study, this small molecule could emerge at the beginning of the 21st century either as a therapeutic agent in itself or as the lead compound for a new class of agents with activity against both M. tuberculosis and HIV.

Tryptophan and Quality of Life in Colorectal Cancer

We tested the hypothesis that reduced tryptophan availability due to immunological stimulation in colorectal cancer impairs quality of life (QoL) by measuring serum tryptophan levels, and correlating them with serum immunological markers and with QoL indices. Serum tryptophan level was significantly reduced in cancer patients compared with healthy controls. Serum tryptophan/kynurenine ratio and neopterin level were significantly increased in cancer, with a significant correlation between the two variables. Reduced serum tryptophan correlated significantly with worse QoL scores. The results support the hypothesis that in colorectal cancer, QoL impairment may be due to serum tryptophan depletion mediated by immunological activation.

Delayed treatment with nicotinamide (vitamin B3) reduces the infarct volume following focal cerebral ischemia in spontaneously hypertensive rats, diabetic and non-diabetic Fischer 344 rats

Since hypertension and/or hyperglycemia are risk factors for stroke, we examined whether the putative neuroprotectant, nicotinamide (NAm), could protect spontaneously hypertensive rats (SHR) or diabetic Fischer 344 rats against focal cerebral ischemia using a model of permanent middle cerebral artery occlusion (MCAo). Intravenous NAm given 2 h after MCAo significantly reduced the infarct volume of SHR (750 mg/kg, 31%, P<0.01) and diabetic (500 mg/kg, 56%, P<0.01) as well as non-diabetic (500 mg/kg, 73%, P<0.01) Fischer 344 rats when compared with saline-injected controls. Thus delayed treatment with NAm protected hypertensive and hyperglycemic rats against a robust model of stroke.