Metabolism of xylitol in healthy subjects and patients with renal disease

Correlation of D-xylose with severity and morbidity-related factors of COVID-19 and possible therapeutic use of D-xylose and antibiotics for COVID-19

The SARS-Cov-2 pandemic that currently affects the entire world has been shown to be especially dangerous in the elderly (≥65 years) and in smokers, with notably strong comorbidity in patients already suffering from chronic diseases, such as Type 2 diabetes, cancers, chronic respiratory diseases, obesity, and hypertension. Inflammation of the lungs is the main factor leading to respiratory distress in patients with chronic respiratory disease and in patients with severe COVID-19. Several studies have shown that inflammation of the lungs in general and Type 2 diabetes are accompanied by the degradation of glycosaminoglycans (GAGs), especially heparan sulfate (HS). Several studies have also shown the importance of countering the degradation of HS in lung infections and Type 2 diabetes. D-xylose, which is the initiating element for different sulfate GAG chains (especially HS), has shown regeneration properties for GAGs. D-xylose and xylitol have demonstrated anti-inflammatory, antiglycemic, antiviral, and antibacterial properties in lung infections, alone or in combination with antibiotics. Considering the existing research on COVID-19 and related to D-xylose/xylitol, this review offers a perspective on why the association between D-xylose and antibiotics may contribute to significantly reducing the duration of treatment of COVID-19 patients and why some anti-inflammatory drugs may increase the severity of COVID-19. A strong correlation with scurvy, based on gender, age, ethnicity, smoking status, and obesity status, is also reviewed. Related to this, the effects of treatment with plants such as Artemisia are also addressed. CHEMICAL COMPOUNDS: D-xylose; xylitol; l-ascorbic Acid; D-glucuronic acid; N-acetylglucosamine; D-N-acetylglucosamine; N-acetylgalactosamine; galactose.

In Vitro Sugar Interference Testing With Amperometric Glucose Oxidase Sensors

BACKGROUND

Electrochemical enzymatic glucose sensors are intended to measure blood or interstitial fluid glucose concentrations. One class of these glucose sensors are continuous glucose monitors (CGMs), indicated for tracking and trending of glucose concentrations in interstitial fluid and as an adjunct to blood glucose testing. Currently approved CGMs employ a glucose oxidase (GOx) electrochemical detection scheme. Potential interfering agents can impact the accuracy of results obtained by glucose sensors, including CGMs.

METHODS

Seven sugars, seven sugar alcohols, and three artificial sweeteners were in vitro screened for interference with amperometric glucose oxidase (GOx) sensors at concentrations greater than physiologic concentrations. Galactose was investigated further at physiologically relevant concentrations using a custom amperometric system. Furthermore, glucose and galactose calibration experiments were conducted to facilitate multiple enzyme kinetic analysis approaches (Michaelis-Menten and Hill equation) to understand the potential source and mechanism of interference from galactose.

RESULTS

Under in vitro testing, except for galactose, xylose and mannose, all screened compounds exhibited interference bias, expressed in mean absolute relative difference (MARD), of ⩽ 20% even at concentrations significantly higher than normal physiologic concentrations. Galactose exhibited, CGM-dependent, MARD of 47-72% and was subjected to further testing. The highest recorded mean relative difference (MRD) was 6.9 ± 1.3% when testing physiologically relevant galactose concentrations (0.1-10 mg/dL). Enzyme kinetic analysis provided calculations of maximum reaction rates ( imax ), apparent Michaelis constants ( Kmapp ), and Hill equation h parameters for glucose and galactose substrates for the enzymes in the CGMs.

CONCLUSION

Under the conditions of in vitro screening, 14 of the 17 compounds did not exhibit measuarable interference. Galactose exhibited the highest interference during screening, but did not substantially interfere with CGMs under the conditions of in vitro testing at physiologically relevant concentrations. Enzyme kinetic analysis conducted with galactose supported the notion that (1) the reactivity of GOx enzyme toward nonglucose sugars and (2) the presence of enzymatic impurities (such as galactose oxidase) are two potential sources for sugar interference with GOx glucose sensors, and thus, should be considered during device development.

Xylitol metabolism in the isolated perfused rat liver

1. Loading the isolated perfused liver from well-fed rats with xylitol (20mm) caused a depletion of adenine nucleotides and P(i) and an accumulation of alpha-glycerophosphate. The ATP content fell to 66% of the control value after 10min and to 32% after 80min. The ADP and AMP contents also fell. After 80min 63% of the total adenine nucleotides and 59% of the P(i) had been lost. 2. The alpha-glycerophosphate content rose from 0.13 to 4.74mumol/g at 10min and reached 8.02mumol/g at 40min. 3. Xylitol was rapidly metabolized, the main products being glucose, lactate and pyruvate. 4. The [lactate]/[pyruvate] ratio in the presence of xylitol rose to 30-40. 5. On perfusion of livers from starved animals the main product of xylitol metabolism was glucose and the mean ratio xylitol removed/glucose formed was 1.29 (corrected for endogenous glucose and lactate production). This is close to the predicted value of 1.2. 6. Evidence is presented indicating that the loss of adenine nucleotides caused by xylitol is not due to the increased ATP consumption but to the accumulation of alpha-glycerophosphate and depletion of P(i). 7. The loss of adenine nucleotides accounts for the hyperuricaemia which can occur after xylitol infusion in man. 8. The relevance of the findings to the clinical use of xylitol as an energy source is discussed.

The osmolyte xylitol reduces the salt concentration of airway surface liquid and may enhance bacterial killing

The thin layer of airway surface liquid (ASL) contains antimicrobial substances that kill the small numbers of bacteria that are constantly being deposited in the lungs. An increase in ASL salt concentration inhibits the activity of airway antimicrobial factors and may partially explain the pathogenesis of cystic fibrosis (CF). We tested the hypothesis that an osmolyte with a low transepithelial permeability may lower the ASL salt concentration, thereby enhancing innate immunity. We found that the five-carbon sugar xylitol has a low transepithelial permeability, is poorly metabolized by several bacteria, and can lower the ASL salt concentration in both CF and non-CF airway epithelia in vitro. Furthermore, in a double-blind, randomized, crossover study, xylitol sprayed for 4 days into each nostril of normal volunteers significantly decreased the number of nasal coagulase-negative Staphylococcus compared with saline control. Xylitol may be of value in decreasing ASL salt concentration and enhancing the innate antimicrobial defense at the airway surface.

Effect of total parenteral nutrition with xylitol on protein and energy metabolism in thermally injured rats

The use of xylitol as an alternative carbohydrate calorie source in total parenteral nutrition may offer unique pharmacologic and nutritional properties in the therapy of the thermally injured. Male Sprague-Dawley rats (250 g) received a 15-second dorsal scald injury (25-30% BSA) and were parenterally fed isovolemic diets (60 ml/day) that provided 200 kcal/kg/d, 9.68 g of amino acids/kg/d, and 23.5% nonprotein calories (NPC) as fat for 3 days. The balance of NPC were provided as dextrose (Dex) or 50% xylitol:50% dextrose (Xyl/Dex). Rectus muscle and liver fractional protein synthetic rates (FSR, %/day), whole body leucine appearance (Flux), oxidation (OX), protein breakdown (PB), and synthesis (PS) were estimated using a 4-hour iv infusion of [1-14C]leucine on day 3. Mean values (+/- SE) for leucine kinetics (mumol leucine/hr/100 g), cumulative nitrogen balance (mg N) and plasma insulin concentration (Table I). (microU/mL). The partial replacement of dextrose calories with xylitol did not significantly alter whole body and tissue leucine kinetics, daily and cumulative nitrogen balance, insulin concentration, and energy expenditure (indirect calorimetry). These data indicate that xylitol may be useful as an alternative carbohydrate calorie source in parenteral nutrition to avoid possible deleterious side effects of glucose overfeeding in the critically ill but did not improve protein metabolism under the conditions of this study.

[Differences in postoperative metabolism after pre- and postoperative beginning of total parenteral nutrition]

In this study we intended to investigate the influence of a 24-h-preoperative total parenteral nutrition (TPN) therapy--10 surgical patients, group 1--compared with the postoperative beginning of TPN--9 surgical patients, group 2--on the postoperative metabolism. Most probably due to preoperatively depleted glycogen storages in G 2, the urinary carbohydrate losses declined more rapidly postoperatively compared with G 1. 45 mMol/l of sodium did not cover the postoperative requirements of G 1. Although we administered 90 mMol/l of potassium/24 h, several patients of G 1 needed an additional substitution. No additional phosphate substitution was necessary in either group. Except for a slight positive balance on the operation day, fluid balance was well balanced on all the other days in G 1. From postoperative day 2 on, G 2 developed a deficit of free water. It could be demonstrated very clear in this study that the postoperative fluid and electrolyte requirements are strongly influenced even by a short-term preoperative fasting period.

Increased serum concentrations of lactic, pyruvic and uric acid and bilibubin after postoperative xylitol infusion

Xylitol has been suggested as a more advantageous calory source for intravenous administration than glucose in certain clinical situation, but the general suitability of intravenous xylitol infusion has not been confirmed. Thirty-middle-aged women were infused with 100 g of xylitol as postoperative fluid therapy after gynaecological laparotomy and general anaesthesia. Another 10 women received 50 g of glucose in a similar manner and served as a reference group. Infusion of xylitol both at the rate of 0.25 g/kg/h (1000 ml 10% xylitol in approx. 8 h) and 0.5 g/kg/h (1000 ml 10% xylitol in approx. 4 h) caused a distinct increase in the serum concentrations of lactic acid, pyruvic acid, and uric acid; such an increase was not seen with glucose infusion. The faster infusion of xylitol also distinctly increased serum bilirubin concentrations. Because of the possibility of lactic acidosis and urate deposits in kidneys, infusion of 100 g or more of xylitol at a rate of 0.25 g/kg/h or faster is not safe for postoperative fluid therapy in routine clinical work.

[Changes in several important metabolic parameters and insulin level during a 7-day total parenteral nutrition under pre- and postoperative conditions]

After the 24 hours preoperative infusion period 0.37% glucose, 0.05% fructose and 1.28% xylitol of the infused amount were excreted in the urine. Postoperatively fructose was the best metabolized energy donator before xylitol and glucose. As a sign of an undisturbed hepatic synthesis of lipoproteins the triglycerides rose up to the 5th postoperative day. During the parenteral nutrition and the additional surgical intervention the cholesterol fell from 192.3 to 128.5 mg/100 ml on the first postoperative day. The infusion solutions caused a rise of the insulin concentration from 23.2 to 46.3 U/l on the operation day. There is a positive nitrogen balance of 3.5 g/24 h on the operation day. The slight negative balance of - 1.15 g/24 h on the first postoperative day is reduced to - 0.61 g/24 h on the postoperative day. The changes of the enzymes LDH, GOT and AP were at normal range. The postoperative changes were due to the surgical intervention. Without a simultaneous change of enzymes, 5 patients had a rise of bilirubin up to 1.1 mg/100 ml. To avoid a too great loose of phosphate during a long-term parenteral nutrition period, it is important to put up a balance.

[Studies on the pharmacokinetics of carbohydrates as a basis for their use in parenteral feeding]

Metabolic effects of glucose, fructose, sorbitol, xylitol and their combinations during intravenous application in men were investigated. The totale and metabolic clearance, the renal and metabolic elimination, the half-time and the turnover rate were measured. For all sugars intravenous long-term infusions from six to twelve hours were performed. Up to a dosage of 0.75 g/kg/h for glucose 0.5 g/kg/h for sorbitol and 0.25 g/kg/h for fructose and xylitol a steady state of substrates and metabolites has been found. If these dosage-limits are exceeded during glucose application a hyperglucosemia, after sorbitol a continous rise in sorbitol blood level, during fructose a rise in lactate and during xylitol infusion clinical side effects occurred. It could be shown that during simultaneous application of glucose, fructose and xylitol the utilization of glucose rises whereas the utilization of fructose and xylitol remain on such levels as if these sugar were infused alone.