Kidney Transplant Low-AGE Diet Study

Study Overview
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Brief Summary
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The purpose of the present study is to test the feasibility of conducting a larger randomised controlled trial (RCT) which will investigate whether a diet low in toxins called advanced glycation end-products (AGEs) decreases skin autofluorescence (SAF; AGE accumulation in the skin) levels and improves heart and circulatory (i.e. cardiovascular) health in persons with a kidney transplant.

Detailed Description
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Kidney transplantation is the optimal treatment option for end-stage kidney disease. Cardiovascular disease is the leading cause of death in persons with kidney disease, even after receiving a kidney transplant. Advanced glycation end-products (AGEs) are compounds that form naturally in our bodies from the chemical reaction of sugars with proteins. If the concentration of AGEs becomes excessive in our bloodstream, they can cause damage to almost every tissue and organ in our bodies, which eventually may lead to an increased risk of cardiovascular death and ill health. AGEs are also found naturally in foods and the content of AGEs in foods is increased considerably by using cooking methods that require high temperatures, such as frying, roasting and grilling. Skin autofluorescence (SAF) is a relatively new, non-invasive, validated and easy to perform technique that measures the skin accumulation of AGEs. It has been reported that kidney transplant recipients have significantly lower SAF levels when compared to persons receiving dialysis; however, these are higher than the general population. Because of the adverse outcomes (e.g. increased risk of death) strongly associated with higher levels of SAF, several options focused on reducing the accumulation of AGEs have been proposed. One of these promising interventions is the reduction of dietary intake of AGEs. It has been suggested that cooking techniques that avoid very high temperatures such as poaching, steaming, stewing and boiling can significantly reduce the AGE content of food when compared to frying, broiling, grilling and roasting. Several studies conducted in healthy overweight and/or obese volunteers, persons with diabetes and in those with chronic kidney disease and performing peritoneal dialysis have reported that reducing dietary AGE intake is associated with a reduction in blood levels of AGEs, suggesting that a low AGE diet may also be associated with a decrease in SAF. Nevertheless, most of the evidence regarding diet modifications to reduce dietary AGE intake is of low quality and therefore further studies are required. Furthermore, this simple dietary intervention has not been previously study in the kidney transplant population. Therefore, if this proposed feasibility study is successful, we will use these findings to identify ways to design future larger research projects to improve the care of persons with a kidney transplant. This is a feasibility study that will be conducted in two parts: Part 1: This will be a randomised controlled trial (RCT) aiming to recruit 40 participants with a functional kidney transplant. Participants will be assigned to either a low AGE diet (intervention group) or a standard diet for persons with a kidney transplant (control group). Participants will be followed-up for 6 months and will receive precise oral and written advice on how to follow the diets. This advice will be tailored to their needs and food preferences.Adherence to both diets will be evaluated by means of a 3-day food diary (2 weekdays and 1 weekend day) every month. The purpose of the control group is to show what would normally happen to AGE levels in the skin and compare it with what happens to AGE levels in the skin when persons with a kidney transplant follow a low AGE diet. Therefore, this will show if the low AGE diet is really responsible of the observations. Potential participants will be approached by the Chief Investigator (a member of the transplant team), during routine follow-up appointments. After the participants have read and understand the Participant Information Sheet (PIS), and had sufficient time (at least 24 hours) to consider their participation in this study, we will ask them to sign a consent form, which shows their willingness to take part. We will then collect information from their medical records or direct interview about their age, ethnicity, medical conditions, educational level, employment and smoking status, medication, alcohol history, and information about their transplant and kidney disease. During the first study assessment, we will: Measure the accumulation of toxins (AGEs) in the skin using a safe, quick (less than five minutes) and painless technique called skin autofluorescence. This involves placing the forearm on a piece of equipment that shines a light on the skin and measures the amount of light that is reflected back. Take routine blood samples and blood pressure. Ask participants to complete a quality of life questionnaire (EQ-5D-5L), a 3-day food diary (2 weekdays and 1 weekend day) to assess energy, fat and protein intake and a validated food frequency questionnaire to evaluate dietary AGE intake. Assess nutritional status using the validated 7-point scale Subjective Global Assessment. Measure weight, height, mid-arm circumference, triceps skinfold thickness, handgrip strength and aortic pulse wave velocity (a measure of cardiovascular health). These same procedures and measurements will be conducted at 3 and 6 months of follow-up. Part 2: Once the RCT (Part 1) has finished, 10 participants from the intervention group and 5 from the control group (ensuring as far as possible that the sample includes a diverse representation of the study population), will be invited to take part in interviews asking questions about the acceptability and tolerability of the intervention (low AGE diet), as well as feedback about the study process. Potential participants will be given or sent an invitation letter and PIS, have the study explained to them and consented separately. The interview will take place at a time and location convenient to the participants and will take about 60 minutes.

Official Title
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A Feasibility Study Exploring the Impact of a Low Advanced Glycation End-product (AGE) Diet on Skin Autofluorescence (SAF) Levels in Kidney Transplant Recipients

Conditions
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Renal Transplant

Intervention / Treatment
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* Other: Diet low in Advanced Glycation End-Products (AGE)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Adults (>18 years) with a functioning (not on dialysis) kidney transplant. More than 12 months post-transplant. Able and willing to give informed consent. Skin Autofluorescence levels above the general population mean value for age. Exclusion Criteria: Persons with dark skin colour (i.e. Fitzpatrick skin colour type 5-6). Persons with malnutrition (Subjective Global Assessment [SGA] score <5). Pregnancy or breast feeding or intending pregnancy. Active infection. Active rejection. Persons with learning difficulties. Prisoners.

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Other
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| No Intervention: Standard diet - Control group<br>The standard diet will include energy intake of 30-35 kcal/kg of ideal body weight (IBW)/day and protein intake of 0.75 g/kg of IBW/day for females and 0.84 g/kg of IBW/day for males | |
| Experimental: Low AGE diet - Intervention group<br>The low AGE diet will be the same as the standard diet in terms of calories (i.e. 30-35 kcal/kg/day) and protein (0.75-0.84 g/kg/day). However, it will reduce the dietary AGE content by changing cooking methods in food preparation to avoid exposure to dry heat such as frying, broiling, grilling and roasting, and to favour cooking with lower temperatures and high-water content as in stewing, steaming, boiling and poaching. In addition, the low-AGE group will be instructed to choose foods with low content of AGEs based on a food choice list that will contain examples of foods commonly available in the UK to be chosen as allowed, moderate intake, or occasional. The goal will be to reduce dietary AGE intake to less than 8000 kU/day. | Other: Diet low in Advanced Glycation End-Products (AGE)<br>* The low AGE diet will primarily consist in reducing the amount of AGEs in foods by changing cooking methods. Participants will also be advice to choose foods low in AGEs; however, the advice will be tailored to participants' food preferences<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Skin autofluorescence (SAF) levels at 6 months | The accumulation of advanced glycation end-products (AGEs) will be assessed by measuring SAF (arbitrary units) using a validated Autofluorescence Reader Standard Unit version 2.4.3 (AGE Reader, DiagnOptics, Groningen, The Netherlands) | 6 months | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Participant adherence to diets | Adherence to the low AGE diet (achieving dietary AGE intake <8000 kilounits [kU]/day) and the standard diet for persons with a kidney transplant will be evaluated by means of a 3-day food diary (2 weekdays and 1 weekend day) every month. | 1-6 months | 
| Mean change in skin autofluorescence levels | Mean change in skin autofluorescence levels (arbitrary units) measured with the AGE Reader. | 3 and 6 months | 
| Mean change in weight | Mean change in body weight (kilograms) | 3 and 6 months | 
| Mean change in aortic pulse wave velocity | Mean change in aortic pulse wave velocity (m/s) assessed using the validated Vicorder device (Skidmore Medical, Bristol, UK) | 3 and 6 months | 
| Mean change in high-sensitive C reactive protein | Mean change in high-sensitive C reactive protein (mg/L) | 3 and 6 months | 
| Mean change in health state score | Mean change in health state score calculated from the European Quality of Life 5-Dimensions questionnaire. The health state score ranges from -0.285 (for the worst health state) to 1 (for the best health state). | 3 and 6 months | 
| Mean change in visual analogue score | Mean change in visual analogue score from the European Quality of Life 5-Dimensions questionnaire. The visual analogue score uses a thermometer-like scale numbered from 0 to 100; the higher the score, the better the health state. | 3 and 6 months |