Introduction

Type 1 diabetes is an autoimmune disorder resulting in the destruction of insulin-producing pancreatic beta cells [1]. Reduced pancreas weights (PWs) at autopsy have been demonstrated in patients with recent-onset type 1 diabetes as well as in those with long-standing disease (reviewed in [1, 2]). Non-invasive imaging has also demonstrated reduced pancreas volume in patients with recent-onset diabetes [3, 4]. The mechanisms underlying reduction in pancreatic size have largely been hypothesised to involve loss of insulinotrophic effects on the exocrine pancreas as islets constitute only 1–2% of the entire pancreas volume [5, 6]. The purpose of this study was to examine the influence of a series of physiological and anthropometric factors, as well as disease duration, on PW in high-quality (i.e. transplant-grade, not autopsy) pancreases obtained from a large number of organ donors with type 1 diabetes, type 2 diabetes and no diabetes. Furthermore, relative PW (RPW; PW [g] / body weight [kg]) was calculated for each pancreatic region (head, body and tail) and the entire organ with subsequent analysis for correlations to age, sex, BMI and diabetes duration.

Methods

Donors

The JDRF Network for Pancreatic Organ donors with Diabetes (nPOD) programme recovered pancreases from organ donors as previously described [7]. Donors without diabetes (controls, n = 86) had no medical history of pancreatic disease and included neonates and children. Donors with type 1 diabetes (n = 90) or type 2 diabetes (n = 40) were classified according to ADA guidelines following medical chart review in concert with islet autoantibody and C-peptide assays, as previously described [7]. Demographic data (age, sex, ethnicity, body weight, BMI) and other clinical findings were recorded from terminal hospital records or data provided by the United Network for Organ Sharing (UNOS) and are summarised in Table 1. Four donors from the Harvard Joslin Medalist programme had pancreases recovered at autopsy and were processed by nPOD [8]. All procedures were conducted in compliance with UNOS and the University of Florida Institutional Review Board requirements, based upon federal guidelines.

Table 1 Donor characteristics
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Pancreas processing

Pancreases were recovered as if for transplantation, shipped by organ courier in iced transport media and cleaned of all extraneous tissues by a licensed pathology assistant according to standard procedures [7]. The pancreas was weighed intact and/or after dividing it into three regions (head, body and tail) by cutting the junction between head and body at the notch and dividing the remaining portion in half for body and tail regions.

Statistical analysis

The primary analysis was based upon RPW as we expected this to minimise the confounding influences of age, sex and BMI on PW, particularly for individuals of younger age with high incidence of type 1 diabetes. BMI (kg/m2) was calculated as weight / (height squared). Body surface area (BSA; m2) was calculated as 0.0235 × height (cm)0.42 × weight (kg)0.51. Similarly, secondary analysis contrasted relative regional weights in the same manner. To control study-wide errors in the primary analysis, the three groups were first compared by ANOVA followed by a Bonferroni corrected contrast between all pairs. Relative regional weights were analysed in the same manner. As a tertiary contrast, we compared the proportions of the total PWs for the three regions across the three donor groups. For analyses not involving RPW, all p values were unadjusted, two-tailed and statistically significant if <0.05. A p value was not calculated if values from two or more cells were equal to 0. Statistical analysis was performed using SAS software version 9.3 (SAS Institute, Cary, NC, USA) and GraphPad Prism (GraphPad Software, San Diego, CA, USA).

Results

Group demographic and clinical variables

A total of 216 donors (n = 86 control, n = 90 type 1 diabetes, n = 40 type 2 diabetes) were prospectively recovered during this study (Table 1). As expected, the ages, heights, weights and BMIs of the donors were significantly different between groups due to the inclusion of very young children in the control group (Table 1). Donors with type 1 diabetes had disease durations of 0–84 years while donors with type 2 diabetes had disease durations ranging from 0 to over 50 years (Table 1). Among those with type 1 diabetes, 15 tested negative for autoantibodies, 36 positive for one and 36 positive for two or more. In those with type 2 diabetes, ten had antibodies against insulin, consistent with medical history of insulin injections and likely reflecting responses to parenteral insulin rather than islet autoantibodies. One donor with type 2 diabetes had low-titre GAD autoantibodies, yet all other findings were consistent with a type 2 diabetes diagnosis (e.g. C-peptide level of 11.55 ng/ml, history of metformin treatment, islet amyloidosis by histopathology [case 6149]).

PW vs RPW

In controls, raw PW correlated closely with age in young donors until adulthood (second order polynomial, R 2 = 0.82, n = 86; Fig. 1a). PW was significantly correlated with body weight (slope = 1.8, R 2 = 0.56, p < 0.001; Fig. 1b) and normalisation of PW to body weight removed any association with age (R 2 = 0.07; Fig. 1a). Raw PWs showed significant differences between all three groups (50.6 ± 35.9 controls, 70.3 ± 17.8 type 1 diabetes, 96.4 ± 16.8 type 2 diabetes).

Fig. 1
figure 1

RPW and diabetes. (a) In control donors without diabetes, PW (g) (triangles) correlated with age while RPW (squares) had no association with age. (b) PW (g) was significantly correlated with body weight (kg) in controls. (c) Donors with type 1 diabetes (T1D, circles) had significantly lower RPW than controls (ND; triangles) and donors with type 2 diabetes (T2D, squares). (d) RPWs by pancreatic region shown for controls (ND; triangles) and donors with T1D (circles) or T2D (squares). Donors with T1D had significantly lower relative regional weights compared with controls and donors with T2D. Donors with T2D had significantly different relative tail weights compared with controls and donors with T1D. (e) RPW did not correlate with disease duration for donors with T1D (circles) or T2D (squares). Data are means ± SD; *p < 0.05 (T1D head vs ND and T2D head; T1D body vs ND and T2D body; T1D tail vs ND and T2D tail; T2D tail vs ND and T1D tail) and ***p < 0.001 (T1D vs ND and T2D donors)

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The RPW was examined to reduce inter-subject factors related to age, sex, BMI and duration of diabetes. None of 11 potential confounding variables were significant for RPW. As such, use of RPW normalised PWs from very young donors to older donors and accounted for differences in sex and BMI.

Reduced RPW and relative regional weights in donors with type 1 diabetes

The RPW for donors with type 1 diabetes was 0.57 ± 0.18 (n = 90) compared with 1.03 ± 0.36 for donors without diabetes (n = 86) and 0.93 ± 0.30 (n = 40) for donors with type 2 diabetes (p < 0.001; Fig. 1c). BSA (m2) was also tested for PW normalisation (PW/BSA); similar results were obtained except that donors with type 2 diabetes had significantly higher PW/BSA compared with controls (electronic supplementary material [ESM] Fig. 1 a, c, e). The BSA was also converted from area to volume (BSA1.5) and used to normalise PWs (PW/BSA1.5); similar proportions were found as for RPW (ESM Fig. 1 b, d, f). Correlations between RPW and PW/BSA1.5 were ≥ 0.94 for all three groups.

Relative weights of each pancreatic region for donors with type 1 diabetes were significantly smaller than the respective regions of controls and donors with type 2 diabetes (Fig. 1d). The relative tail weights were also significantly different between all groups (Fig. 1d).

Diabetes duration and C-peptide levels do not correlate with RPW

RPW was not significantly associated with duration of diabetes for donors with type 1 diabetes or type 2 diabetes, even for those with diabetes of short duration (Fig. 1e). RPW did not significantly correlate with C-peptide levels or diabetes duration in donors with type 1 diabetes who had detectable levels (ESM Fig. 2 a–f). Interestingly, raw PWs in controls were significantly though weakly correlated with C-peptide levels (r = 0.33, p < 0.01, ESM Fig. 2e).

Discussion

Herein, we note that RPW allows for examination of PW differences between study subject groups despite differences in age, ethnicity or body weight. In donors with type 1 diabetes, RPW was only 55% that of donors without diabetes. Strikingly, this loss in weight was apparent at or near disease onset and was minimally altered in those with disease duration of several decades. This is an extremely interesting finding in that it suggests a different concept from the widely held notion that the reduced PW is a result of long-term insulin absence.

Our observation of pronounced PW loss in recent-onset type 1 diabetes agrees with the findings of several studies and supports the hypothesis that underlying mechanisms associated with loss in PW precede diagnosis [3, 4, 9]. The cross-sectional nature of our study does not preclude an alternative hypothesis, namely, that persons at risk for type 1 diabetes have smaller pancreases due to undefined genetic, maternal or environmental factors (reviewed in [1]). Future longitudinal studies in living individuals at high risk for type 1 diabetes and utilising advanced imaging techniques should be used to address issues of pancreatic size in relationship to type 1 diabetes duration and treatment (reviewed in [3]). Here too, studies in type 1 diabetes that would bring clarity to issues beyond those of weight and size alone, including beta cell mass and exocrine inflammation, would also be valuable.

Additional novelty in this report resides in our findings on altered pancreatic regional weights. Specifically, the decline in regional PWs are consistent with primary loss of the pancreatic dorsal lobe, comprised of the major portion of the head and entire body and tail regions, while the ventral lobe (i.e. small portion of head region and most of the uncinate process) remains less affected [10]. In summary, our hope is that the efforts reported herein to normalise PW across a wide age range could stimulate additional studies to further define the clinical and pathogenic significance of reduced PW in type 1 diabetes.