A simple method for plasma total vitamin C analysis suitable for routine clinical laboratory use.

BACKGROUND: In-hospital hypovitaminosis C is highly prevalent but almost completely unrecognized. Medical awareness of this potentially important disorder is hindered by the inability of most hospital laboratories to determine plasma vitamin C concentrations. The availability of a simple, reliable method for analyzing plasma vitamin C could increase opportunities for routine plasma vitamin C analysis in clinical medicine. METHODS: Plasma vitamin C can be analyzed by high performance liquid chromatography (HPLC) with electrochemical (EC) or ultraviolet (UV) light detection. We modified existing UV-HPLC methods for plasma total vitamin C analysis (the sum of ascorbic and dehydroascorbic acid) to develop a simple, constant-low-pH sample reduction procedure followed by isocratic reverse-phase HPLC separation using a purely aqueous low-pH non-buffered mobile phase. Although EC-HPLC is widely recommended over UV-HPLC for plasma total vitamin C analysis, the two methods have never been directly compared. We formally compared the simplified UV-HPLC method with EC-HPLC in 80 consecutive clinical samples. RESULTS: The simplified UV-HPLC method was less expensive, easier to set up, required fewer reagents and no pH adjustments, and demonstrated greater sample stability than many existing methods for plasma vitamin C analysis. When compared with the gold-standard EC-HPLC method in 80 consecutive clinical samples exhibiting a wide range of plasma vitamin C concentrations, it performed equivalently. CONCLUSION: The easy set up, simplicity and sensitivity of the plasma vitamin C analysis method described here could make it practical in a normally equipped hospital laboratory. Unlike any prior UV-HPLC method for plasma total vitamin C analysis, it was rigorously compared with the gold-standard EC-HPLC method and performed equivalently. Adoption of this method could increase the availability of plasma vitamin C analysis in clinical medicine.

Appropriate vitamin D loading regimen for patients with advanced lung cancer.

BACKGROUND: Most patients attending cancer clinics have hypovitaminosis D. Correcting or preventing this abnormal condition could mitigate the emotional and physical complications of their disease, but clinical trials of vitamin D therapy in this setting are hindered by the unavailability of safe, effective and practical loading dose regimens. METHODS: In this single arm open-label pharmacokinetic trial, outpatients with advanced lung cancer consumed 20,000 IU vitamin D daily with the largest meal of the day for 14 days followed by 10,000 IU per day for a further 7 days. Plasma concentrations of 25-hydroxyvitamin D [25(OH)D], parathyroid hormone, calcium, vitamin C and C-reactive protein were measured on protocol days 0, 14 and 21, and serum vitamin D binding protein (VDBP) concentrations on days 0 and 21. As a secondary objective, preliminary information was obtained regarding clinical effects of rapid vitamin D loading on mood and symptoms by administering appropriate questionnaires two times at baseline and after 14 and 21 days of vitamin D therapy. RESULTS: Of the 91 patients enrolled in the study, 85 % had hypovitaminosis D and 41 % had hypovitaminosis C. Plasma VDBP concentrations were in the normal range. The vitamin D load increased the average plasma 25(OH)D concentration to 116 ± 34 nmol/L (mean ± SD); the median concentration was 122 nmol/L (interquartile range 103-134); VDBP concentrations did not change. Final plasma 25(OH)D concentrations were subnormal (<75 nmol/L) for 13 % of the patients and sub-target (<120 nmol/L) for 44 % of them. In most cases, subnormal and sub-target 25(OH)D concentrations were attributable to obesity and/or a low baseline 25(OH)D concentration. Mood and symptom scores did not change significantly throughout the 3-week protocol. CONCLUSION: Hypovitaminosis D and C are very common in outpatients with advanced lung cancer. A vitamin D load of 20,000 IU per day for 14 days failed to achieve the target concentration in 44 % of the participants in this trial. These results suggest that a loading dose of 30,000 IU per day for 14 days would be safe and effective for patients who are obese or at risk of severe hypovitaminosis D. The preliminary nature of the study design, and the failure to achieve target 25(OH)D concentrations for a large proportion of the patients, do not allow any firm conclusion about the clinical effects of correcting hypovitaminosis D in this patient population. Nevertheless, no evidence was obtained that partial correction of hypovitaminosis D greatly improved mood, reduced distress or relieved cancer-related symptoms. This trial was registered at clinicaltrials.gov as NCT01631526.

The need for consistent criteria for identifying malnutrition.

The lack of consistent criteria for diagnosing malnutrition and protein-energy malnutrition (PEM) creates problems in educating medical students and physicians, setting the parameters for observational and controlled clinical trials, and formulating clinical guidelines. There is no validated formal definition of malnutrition (or PEM), and the tools that have been developed to screen for it, or diagnose it, vary in their agreement. I make the following suggestions. First, avoid unqualified use of the term 'malnutrition', as it is ambiguous. Second, carefully distinguish between screening and diagnosis, which have different aims and implications. Third, consider the notion that in medicine the diagnosis of PEM is reached by 'narrative-interpretive' reasoning, which regards the disease as a pathophysiological entity in a specific clinical context. I recommend that the concept of PEM as a disease (not a score) be imbedded in teaching and the practice of medicine, and in the design of clinical trials and the setting of guidelines. Fourth, disagreements in screening-derived risk scores and uncertainty in diagnosis are difficult to avoid, but only in the grey zone. It would be prudent, at least until the greater medical world considers the nutritional paradigm plausible enough to invest in it, to enroll only patients who have unambiguously diagnosed PEM in prospective trials with hard clinical endpoints.

Vitamin C deficiency in a university teaching hospital.

OBJECTIVES: There is almost no information regarding the vitamin C status of patients treated in Canadian and American hospitals. We determined the prevalence and predictors of vitamin C deficiency in patients hospitalized on the acute-care wards of a Canadian teaching hospital, and tracked their plasma vitamin C concentrations while they were there. METHODS: This was a population-based cross-sectional and time course survey of 149 medical patients shortly after admission to a university teaching hospital. The procedure for sample handling, storage and analysis was validated by measuring the vitamin C concentrations of a reference sample of 141 presumably well nourished people and comparing the results with published norms. RESULTS: In keeping with published norms, 13% of people in the reference group had a subnormal vitamin C concentration (<28.4 micromol/L) and 3% were vitamin C deficient (<11.4 micromol/L). By contrast, 60% of hospitalized patients had a subnormal vitamin C concentration and 19% were deficient. A history of inadequate nutrition or failure to use a vitamin supplement prior to admission, low serum albumin, and male sex predicted plasma vitamin C deficiency, whereas use of a vitamin supplement prior to admission was associated with adequate vitamin C status in hospital. In a second measurement, obtained in 52 patients after an average of 17 days in hospital, vitamin C status had not improved. CONCLUSIONS: Vitamin C deficiency is prevalent and sustained in patients in a Canadian teaching hospital. The abnormality can be prevented by providing a diet sufficient in vitamin C or by prescribing a multiple vitamin tablet.

High-Protein Hypocaloric Nutrition for Non-Obese Critically Ill Patients.

High-protein hypocaloric nutrition, tailored to each patient's muscle mass, protein-catabolic severity, and exogenous energy tolerance, is the most plausible nutrition therapy in protein-catabolic critical illness. Sufficient protein provision could mitigate the rapid muscle atrophy characteristic of this disease while providing urgently needed amino acids to the central protein compartment and sites of tissue injury. The protein dose may range from 1.5 to 2.5 g protein (1.8-3.0 g free amino acids)/kg dry body weight per day. Nutrition should be low in energy (≈70% of energy expenditure or ≈15 kcal/kg dry body weight per day) because efforts to match energy provision to energy expenditure are physiologically irrational, risk toxic energy overfeeding, and have repeatedly failed in large clinical trials to demonstrate clinical benefit. The American Society for Parenteral and Enteral Nutrition currently suggests high-protein hypocaloric nutrition for obese critically ill patients. Short-term high-protein hypocaloric nutrition is physiologically and clinically sensible for most protein-catabolic critically ill patients, whether obese or not.

Will We Ever Agree on Protein Requirements in the Intensive Care Unit?

The precise value of the normal adult protein requirement has long been debated. For many reasons-one of them being the difficulty of carrying out long-term nutrition experiments in free-living people-uncertainty is likely to persist indefinitely. By contrast, the controlled environment of the intensive care unit and relatively short trajectory of many critical illnesses make it feasible to use hard clinical outcome trials to determine protein requirements for critically ill patients in well-defined clinical situations. This article suggests how the physiological principles that underlie our understanding of normal protein requirements can be incorporated into the design of such clinical trials. The main focus is on 3 principles: (1) the rate of body nitrogen loss roughly predicts an individual's minimum protein requirement and is thus essential to measure to identify individual patients and clinical situations in which the minimum protein requirement is importantly increased, (2) existing muscle mass sets an upper limit on the rate at which amino acids can be mobilized from muscle for transfer to central proteins and sites of injury and is thus important to monitor to identify patients who are at greatest risk of protein deficiency-related adverse outcomes, and (3) negative energy balance increases the dietary protein requirement, so calorie-deprived patients-whether obese or not-should be enrolled in hard clinical outcome trials that compare the current practice of "permissive underfeeding" (underprovision of all nutrients, including protein) with hypocaloric nutrition supplemented by a suitably generous amount of protein.

Summary Points and Consensus Recommendations From the International Protein Summit.

The International Protein Summit in 2016 brought experts in clinical nutrition and protein metabolism together from around the globe to determine the impact of high-dose protein administration on clinical outcomes and address barriers to its delivery in the critically ill patient. It has been suggested that high doses of protein in the range of 1.2-2.5 g/kg/d may be required in the setting of the intensive care unit (ICU) to optimize nutrition therapy and reduce mortality. While incapable of blunting the catabolic response, protein doses in this range may be needed to best stimulate new protein synthesis and preserve muscle mass. Quality of protein (determined by source, content and ratio of amino acids, and digestibility) affects nutrient sensing pathways such as the mammalian target of rapamycin. Achieving protein goals the first week following admission to the ICU should take precedence over meeting energy goals. High-protein hypocaloric (providing 80%-90% of caloric requirements) feeding may evolve as the best strategy during the initial phase of critical illness to avoid overfeeding, improve insulin sensitivity, and maintain body protein homeostasis, especially in the patient at high nutrition risk. This article provides a set of recommendations based on assessment of the current literature to guide healthcare professionals in clinical practice at this time, as well as a list of potential topics to guide investigators for purposes of research in the future.

Intravenously administered vitamin C as cancer therapy: three cases.

Early clinical studies showed that high-dose vitamin C, given by intravenous and oral routes, may improve symptoms and prolong life in patients with terminal cancer. Double-blind placebo-controlled studies of oral vitamin C therapy showed no benefit. Recent evidence shows that oral administration of the maximum tolerated dose of vitamin C (18 g/d) produces peak plasma concentrations of only 220 micromol/L, whereas intravenous administration of the same dose produces plasma concentrations about 25-fold higher. Larger doses (50-100 g) given intravenously may result in plasma concentrations of about 14,000 micromol/L. At concentrations above 1000 micromol/L, vitamin C is toxic to some cancer cells but not to normal cells in vitro. We found 3 well-documented cases of advanced cancers, confirmed by histopathologic review, where patients had unexpectedly long survival times after receiving high-dose intravenous vitamin C therapy. We examined clinical details of each case in accordance with National Cancer Institute (NCI) Best Case Series guidelines. Tumour pathology was verified by pathologists at the NCI who were unaware of diagnosis or treatment. In light of recent clinical pharmacokinetic findings and in vitro evidence of anti-tumour mechanisms, these case reports indicate that the role of high-dose intravenous vitamin C therapy in cancer treatment should be reassessed.

Human Protein and Amino Acid Requirements.

Human protein and amino acid nutrition encompasses a wide, complex, frequently misunderstood, and often contentious area of clinical research and practice. This tutorial explains the basic biochemical and physiologic principles that underlie our current understanding of protein and amino acid nutrition. The following topics are discussed: (1) the identity, measurement, and essentiality of nutritional proteins; (2) the definition and determination of minimum requirements; (3) nutrition adaptation; (4) obligatory nitrogen excretion and the minimum protein requirement; (5) minimum versus optimum protein intakes; (6) metabolic responses to surfeit and deficient protein intakes; (7) body composition and protein requirements; (8) labile protein; (9) N balance; (10) the principles of protein and amino acid turnover, including an analysis of the controversial indicator amino acid oxidation technique; (11) general guidelines for evaluating protein turnover articles; (12) amino acid turnover versus clearance; (13) the protein content of hydrated amino acid solutions; (14) protein requirements in special situations, including protein-catabolic critical illness; (15) amino acid supplements and additives, including monosodium glutamate and glutamine; and (16) a perspective on the future of protein and amino acid nutrition research. In addition to providing practical information, this tutorial aims to demonstrate the importance of rigorous physiologic reasoning, stimulate intellectual curiosity, and encourage fresh ideas in this dynamic area of human nutrition. In general, references are provided only for topics that are not well covered in modern textbooks.

Nutrition in critical illness: a current conundrum.

Critically ill people are unable to eat. What's the best way to feed them? Nutrition authorities have long recommended providing generous amounts of protein and calories to critically ill patients, either intravenously or through feeding tubes, in order to counteract the catabolic state associated with this condition. In practice, however, patients in modern intensive care units are substantially underfed. Several large randomized clinical trials were recently carried out to determine the clinical implications of this situation. Contradicting decades of physiological, clinical, and observational data, the results of these trials have been claimed to justify the current practice of systematic underfeeding in the intensive care unit. This article explains and suggests how to resolve this conundrum.

Cobalamin dose regimen for maximum homocysteine reduction in end-stage renal disease.

Plasma total homocysteine (tHcy) concentrations are markedly increased in end-stage renal disease and only partially corrected by folic acid supplementation. We and others have reported that cobalamin, administered parenterally, reduces plasma tHcy substantially below the lowest concentrations attainable with folic acid. We have now carried out a randomized controlled clinical trial to compare the plasma Hcy-lowering effect of 3 intravenous cyanocobalamin dose regimens in maintenance hemodialysis patients: 1 mg postdialysis every 28, 14, and 7 days in addition to routine oral vitamin B supplementation. All patients in the hemodialysis unit where the study was carried out routinely received 1 mg intravenous cyanocobalamin every month, so participants who were randomized to receive the vitamin every 28 days simply continued with their existing treatment program. Serum cobalamin and plasma tHcy concentrations in the control group did not change over the course of the study. As measured after 8 weeks of therapy, intravenous cyanocobalamin every 14 days increased serum cobalamin approximately 2.5-fold and reduced plasma tHcy by 11.5% ( P = .035) below the concentration previously attained with monthly administration, whereas treatment every 7 days increased serum cobalamin concentrations approximately 5-fold and reduced plasma tHcy by 11.0% ( P = .013). These results show that intravenous cyanocobalamin at 7- or 14-day intervals reduces plasma tHcy concentrations of hemodialysis patients below the levels brought about by prior long-term administration every 4 weeks and confirms that plasma tHcy lowering with parenteral cobalamin is a true pharmacological effect and not merely correction of a latent deficiency state.

Comparative effects of hydroxocobalamin and cyanocobalamin on plasma homocysteine concentrations in end-stage renal disease.

End-stage renal disease (ESRD) is associated with marked hyperhomocysteinemia which is only partially corrected by folic acid and pyridoxine supplementation. We and others have reported that various forms of parenteral cobalamin reduce plasma total homocysteine (tHcy) concentrations of patients with ESRD substantially below the lowest levels attainable with folic acid. We here report a 16-week randomized controlled crossover trial which directly compared the Hcy-lowering effect of intravenous hydroxocobalamin (HC) with that of cyanocobalamin (CC). Folic acid- and vitamin B12-replete maintenance hemodialysis patients were randomly assigned to receive either 1 mg intravenous HC weekly for 8 weeks followed by CC for a further 8 weeks, or CC for 8 weeks followed by HC for 8 weeks. Hydroxocobalamin increased serum cobalamin concentrations 40-fold, whereas CC increased them only 10-fold, but both treatments reduced plasma tHcy concentrations similarly by 33% (P < .001). Crossover to the alternate form of the vitamin greatly affected the serum cobalamin concentration but was without further effect on the plasma tHcy concentration. These results confirm that weekly cobalamin injections lower plasma tHcy concentrations of hemodialysis patients well below the level attainable with folic acid. Hydroxocobalamin and CC are equipotent despite producing very different serum cobalamin concentrations.

High-dose intravenous vitamin C combined with cytotoxic chemotherapy in patients with advanced cancer: a phase I-II clinical trial.

BACKGROUND: Biological and some clinical evidence suggest that high-dose intravenous vitamin C (IVC) could increase the effectiveness of cancer chemotherapy. IVC is widely used by integrative and complementary cancer therapists, but rigorous data are lacking as to its safety and which cancers and chemotherapy regimens would be the most promising to investigate in detail. METHODS AND FINDINGS: We carried out a phase I-II safety, tolerability, pharmacokinetic and efficacy trial of IVC combined with chemotherapy in patients whose treating oncologist judged that standard-of-care or off-label chemotherapy offered less than a 33% likelihood of a meaningful response. We documented adverse events and toxicity associated with IVC infusions, determined pre- and post-chemotherapy vitamin C and oxalic acid pharmacokinetic profiles, and monitored objective clinical responses, mood and quality of life. Fourteen patients were enrolled. IVC was safe and generally well tolerated, although some patients experienced transient adverse events during or after IVC infusions. The pre- and post-chemotherapy pharmacokinetic profiles suggested that tissue uptake of vitamin C increases after chemotherapy, with no increase in urinary oxalic acid excretion. Three patients with different types of cancer experienced unexpected transient stable disease, increased energy and functional improvement. CONCLUSIONS: Despite IVC's biological and clinical plausibility, career cancer investigators currently ignore it while integrative cancer therapists use it widely but without reporting the kind of clinical data that is normally gathered in cancer drug development. The present study neither proves nor disproves IVC's value in cancer therapy, but it provides practical information, and indicates a feasible way to evaluate this plausible but unproven therapy in an academic environment that is currently uninterested in it. If carried out in sufficient numbers, simple studies like this one could identify specific clusters of cancer type, chemotherapy regimen and IVC in which exceptional responses occur frequently enough to justify appropriately focused clinical trials. TRIAL REGISTRATION: ClinicalTrials.gov NCT01050621.

Protein and energy provision in critical illness.

It has recently been recommended that parenterally fed, critically ill patients should receive considerably less energy than the 36 kcal.kg(-1).d(-1) customarily received in earlier years and that mixed amino acid infusions not exceed 1.5 g.kg(-1).d(-1). The implications of these recommendations should be considered carefully, especially for patients with low body weight. Any sizeable reduction in energy provision will lead to negative energy balance in at least some patients, and negative energy balance is known to increase protein requirements. The optimal rate of amino acid delivery for underfed, critically ill patients is not well defined and could well exceed 1.5 g.kg(-1).d(-1). In addition, there are good reasons to suspect that the safe protein requirement of severely underweight, critically ill patients is >1.5 g.kg(-1).d(-1), even when adequate energy is provided.

Homocysteine remethylation and trans-sulfuration.

The plasma homocysteine (Hcy) concentration represents the balance between its entry and removal from the circulation. This understanding has stimulated efforts to elucidate the causes of hyperhomocysteinemia by measuring plasma Hcy turnover. However, these studies have been performed under steady-state conditions, which do not allow for conclusions about the type and severity of the metabolic blocks that cause metabolites to accumulate. Failure to appreciate this has led to some confusion in the literature dealing with whole body Hcy metabolism.

Hydroxocobalamin reduces hyperhomocysteinemia in end-stage renal disease.

Renal failure causes hyperhomocysteinemia, an important risk factor for cardiovascular disease and venous access thrombosis in end-stage renal disease (ESRD). Folic acid is necessary for homocysteine (Hcy) metabolism, and therapy with 1 mg/d or more of folic acid reduces plasma total Hcy (tHcy) concentrations in ESRD, although seldom to normal. In contrast to folic acid, the Hcy-lowering effect of vitamin B(12) has not been well studied in ESRD. We performed a prospective randomized controlled clinical trial involving 24 maintenance hemodialysis patients with normal or supranormal serum folate and vitamin B(12) concentrations who received either standard therapy, which included 5 to 6 mg folic acid, 5 to 10 mg pyridoxine, and 6 to 10 microg oral vitamin B(12) per day, or standard therapy plus 1 mg hydroxocobalamin administered subcutaneously once per week after dialysis. Plasma tHcy and serum methylmalonic acid (MMA) concentrations were measured before and after 8 and 16 weeks of continuous treatment. Hydroxocobalamin reduced plasma tHcy by an average of 32% (P <.005) and serum MMA by an average of 19% (P <.001). The Hcy-lowering effect of hydroxocobalamin was independent of baseline serum vitamin B(12), folic acid, and MMA concentrations. Patients with higher baseline plasma tHcy concentrations had the greatest response (r = 0.80; P <.002). These results show that parenteral hydroxocobalamin reduces plasma tHcy dramatically in vitamin B(12)-replete hemodialysis patients. Persons with considerable persisting hyperhomocysteinemia despite high-dose folic acid therapy are likely to respond to the addition of hydroxocobalamin, irrespective of their serum vitamin B(12) concentrations.