Lesions of the Pancreatic Islets Produced in Cats by Administration of Glucose

Feline comorbidities: Pathophysiology and management of the obese diabetic cat

PRACTICAL RELEVANCE

Up to 40% of the domestic feline population is overweight or obese. Obesity in cats leads to insulin resistance via multiple mechanisms, with each excess kilogram of body weight resulting in a 30% decline in insulin sensitivity. Obese, insulin-resistant cats with concurrent beta-cell dysfunction are at risk of progression to overt diabetes mellitus.

APPROACH TO MANAGEMENT

In cats that develop diabetes, appropriate treatment includes dietary modification to achieve ideal body condition (for reduction of insulin resistance), and optimization of diet composition and insulin therapy (for glycemic control and the chance of diabetic remission). Initially, as many obese cats that become diabetic will have lost a significant amount of weight and muscle mass by the time of presentation, some degree of diabetic control should be attempted with insulin before initiating any caloric restriction. Once body weight has stabilized, if further weight loss is needed, a diet with ≤ 12-15% carbohydrate metabolizable energy (ME) and >40% protein ME should be fed at 80% of resting energy requirement for ideal weight, with the goal of 0.5-1% weight loss per week. Other approaches may be necessary in some cats that need either substantial caloric restriction or do not find low carbohydrate diets palatable. Long-acting insulins are preferred as initial choices and oral antidiabetic drugs can be used in combination with diet if owners are unable or unwilling to give insulin injections. Glucagon-like peptide-1 (GLP-1) agonists have recently been investigated for use as adjunctive treatment in diabetic cats and sodium-glucose cotransporter-2 (SGLT2) inhibitors are currently being evaluated in clinical trials.

EVIDENCE BASE

The information in this review is drawn from: epidemiological studies on obesity prevalence; prospective longitudinal studies of development of insulin resistance with obesity; randomized controlled studies; and expert opinion regarding the effect of diet on diabetes management in cats.

The role of total pancreatectomy and islet autotransplantation for chronic pancreatitis

Total pancreatectomy and islet autotransplantation are done for chronic pancreatitis with intractable pain when other treatment measures have failed, allowing insulin secretory capacity to be preserved, minimizing or preventing diabetes, while at the same time removing the root cause of the pain. Since the first case in 1977, several series have been published. Pain relief is obtained in most patients, and insulin independence preserved long term in about a third, with another third having sufficient beta cell function so that the surgical diabetes is mild. Islet autotransplantation has been done with partial or total pancreatectomy for benign and premalignant conditions. Islet autotransplantation should be used more widely to preserve beta cell mass in major pancreatic resections.

Feline diabetes mellitus: low carbohydrates versus high fiber?

Treatment of diabetes mellitus (DM) in the cat relies primarily on the adequate insulin therapy and controlled dietary intake. The goals of managing DM in the cat have changed from attaining glycemic control to achieving diabetic remission (transient diabetes) in a large proportion of cases. Remission rates of up to 68% have been published. The used of low-carbohydrate foods for cats improves the odds of achieving diabetic remission by fourfold. Nonetheless, some cats show an improved response to high-fiber food. Clinical judgement, trial, and personal preference to currently dictate which diet to offer an individual animal.

Pancreas and islet cell transplantation

Transplantation of the pancreas or islet cells constitutes surgical treatment for patients with type 1 diabetes mellitus. Pancreas transplantation is now an established procedure for the surgical treatment of diabetes mellitus. Islet cell transplantation has the potential to be the procedure of choice once it becomes more routine because of the minimal surgery involved. Included in this chapter are the pathophysiology of diabetes, rationale for transplantation, and the surgical procedure itself.

Transplant options for patients undergoing total pancreatectomy for chronic pancreatitis

BACKGROUND

Total pancreatectomy to treat chronic pancreatitis is associated with severe diabetic control problems in 15% to 75% of patients, causing up to 50% of deaths late postoperatively. We report our experience with islet autotransplants at the time of, or with pancreas allotransplants after, total pancreatectomy.

STUDY DESIGN

Between February 1, 1977, and June 30, 2003, we performed 112 islet autotransplants at the time of total pancreatectomy; we also performed 20 pancreas allotransplants in 13 patients who had already undergone total pancreatectomy months to years earlier.

RESULTS

Islet autotransplants at the time of total pancreatectomy in patients who had not had previous operations on the body and tail of the pancreas were associated with a high islet yield (>2,500 islet equivalents/kg body weight), and >70% of the recipients achieved complete insulin independence. In contrast, a previous distal pancreatectomy or a Puestow drainage procedure was associated with a low islet yield in 75% of them and with complete insulin independence in <20%. A pancreas allotransplant after total pancreatectomy was not associated with any transplant-related mortality at 1 and 3 years posttransplant. The pancreas graft survival rate at 1 year posttransplant was 77% with tacrolimus-based immunosuppression (versus 67% with cyclosporine). Enteric (over bladder) drainage was preferred to manage exocrine graft secretions, to cure pancreatectomy-induced endocrine and exocrine insufficiency.

CONCLUSIONS

Our series shows that pancreas allotransplants can be performed without transplant-related mortality and, when tacrolimus-based immunosuppression is used, with 1-year pancreas graft survival rates >75%. In contrast to a simultaneous islet autotransplant, a pancreas allotransplant has the disadvantage of requiring lifelong immunosuppression, but the advantage of not only curing endocrine but also exocrine insufficiency. Both transplant options, if successful, improve the recipient's quality of life.

Total pancreatectomy with islet cell autotransplantation: anesthetic implications

STUDY OBJECTIVE

To make recommendations for the perioperative management of patients undergoing total pancreatectomy with islet cell autotransplantation.

DESIGN

Retrospective review.

SETTING

University hospital.

PATIENTS

41 patients undergoing total pancreatectomy with autologous islet cell transplantation for chronic pancreatitis from 1977 to 1996.

INTERVENTIONS

The charts and anesthetic records were reviewed, specifically investigating the changes in portal venous pressure, blood pressure (BP), and central venous pressure with islet cell injection. The records also were examined for blood glucose levels, type of fluids administered, blood loss, and postoperative complications.

MEASUREMENTS AND MAIN RESULTS

Injection of islet cells into the portal vein caused a significant increase in portal venous pressures (8.5 +/- 4.8 to 27 +/- 16 cm/H2O; p < 0.001), which remained elevated at the end of injection (23 +/- 12 cm/H2O; p < 0.001). Central venous pressures also increased a small amount (9.3 +/- 4.3 to 10.6 +/- 5.8 mmHg; p < 0.05). In contrast, systolic blood pressures (SBPs) fell with administration of the islet cells (110 +/- 15 to 103 +/- 17 mmHg; p < 0.01), but SBP recovered in most patients at the end of injection (106 +/- 16 mmHg; p = NS). However, 6 patients (14.6%) required vasopressors to maintain adequate BPs. Blood glucose levels were significantly higher immediately prior to islet cell infusion in patients who had received dextrose-containing solutions than those who did not (246 +/- 80 vs. 176 +/- 43 gm/dl; p = 0.002). Median blood loss was 2000 ml (range 350 to 12,000 ml), and most patients (95.1%) required blood transfusions.

CONCLUSION

Although total pancreatectomy with islet cell autotransplantation is a difficult operation, with significant blood loss, most patients tolerate surgery and injection of islet cells into their portal system without hemodynamic instability. Glucose-containing solutions should not be administered to patients prior to islet cell infusion because hyperglycemia, which can damage islet cells, may result.

Prolonged exposure of human pancreatic islets to high glucose concentrations in vitro impairs the beta-cell function

The aim of the present study was to clarify whether prolonged in vitro exposure of human pancreatic islets to high glucose concentrations impairs the function of these cells. For this purpose, islets isolated from adult cadaveric organ donors were cultured for seven days in RPMI 1640 medium supplemented with 10% fetal calf serum and containing either 5.6, 11, or 28 mM glucose. There was no glucose-induced decrease in islet DNA content or signs of morphological damage. However, islets cultured at 11 or 28 mM glucose showed a 45 or 60% decrease in insulin content, as compared to islets cultured at 5.6 mM glucose. Moreover, when such islets were submitted to a 60-min stimulation with a low (1.7 mM) followed by a high (16.7 mM) concentration of glucose, the islets cultured at 5.6 mM glucose showed a higher insulin response to glucose than those of the two other groups. Islets cultured at the two higher glucose concentrations showed increased rates of insulin release in the presence of low glucose, and a failure to enhance further the release in response to an elevated glucose level. Islets cultured at 28 mM glucose showed an absolute decrease in insulin release after stimulation with 16.7 mM glucose, as compared to islets cultured at 5.6 mM glucose. The rates of glucose oxidation, proinsulin biosynthesis, and total protein biosynthesis were similar in islets cultured at 5.6 or 11 mM glucose, but they were decreased in islets cultured at 28 mM glucose. These combined results suggest that lasting exposure to high glucose concentrations impairs the function of human pancreatic islets.

Natural history of intrahepatic canine islet cell autografts

We have serially followed the function of intrahepatic canine islet autografts in 15 beagle dogs for up to 24 mo. Of these, only 20% sustained normal levels of fasting blood glucose for greater than 15 mo posttransplant. Failure of autograft function was accompanied by a preferential loss of well-granulated beta cells in the engrafted islets. The chronic stimulation of an initially marginal intrahepatic beta-cell mass ultimately resulted in metabolic deterioration and loss of beta cells below the minimal threshold required to maintain normal fasting blood glucose levels. It is possible that transplantation of a larger mass of islets would result in indefinite graft function in dogs. However, it remains to be demonstrated in larger mammals, including humans, whether an islet cell mass that is initially adequate in a heterotropic site such as the liver can remain functionally competent over a prolonged period.

Modulation of proinsulin messenger RNA after partial pancreatectomy in rats. Relationships to glucose homeostasis

These studies of partial pancreatectomy assess pancreatic proinsulin messenger RNA (mRNA) levels as an index of in vivo insulin biosynthesis, and show relationships to glucose homeostasis. Rats were subjected to sham operation, 50% pancreatectomy (Px), or 90% Px, and were examined after 1, 3, or 14 wk. Proinsulin mRNA was measured by dot hybridization to complementary DNA. After 50% Px there was a nearly complete adaptation of proinsulin mRNA. After 90% Px a marked increase of proinsulin mRNA occurred, but it was insufficient and it was not maintained with time. The deficit in insulin production is related to development of hyperglycemia. Sham-operated controls showed no worsening of fasting or fed blood glucose or of intraperitoneal glucose tolerance within the period of observation. Total proinsulin mRNA and pancreatic insulin content rose in proportion to body weight. 50% Px produced no change from controls in body weight or blood glucose. The concentration of proinsulin mRNA in the 50% pancreatic remnant paralleled that of controls after 1 and 3 wk, but then increased after 14 wk, such that total proinsulin mRNA approached control levels. This adaptive response was reflected by changes in serum insulin, but not by pancreatic insulin content, which was only 30% of control after 14 wk. Intraperitoneal glucose tolerance was impaired mildly, and did not worsen with time after pancreatectomy. 90% Px led to elevated fed blood glucose and reduced serum insulin after 3 wk, and fasting hyperglycemia was seen after 14 wk. Proinsulin mRNA concentration in the 10% pancreatic remnant showed an adaptive increase after 1 and 3 wk, such that total proinsulin mRNA reached 40% of control. After 14 wk, however, remnant proinsulin mRNA concentration was no longer increased; total proinsulin mRNA and pancreatic insulin content were severely reduced. Intraperitoneal glucose tolerance was impaired more dramatically than with the 50% Px animals, and worsened with time after operation. These observations indicate ability to increase proinsulin mRNA levels as an adaptation to pancreatectomy. Insufficiency of this adaptation is associated with the development of hyperglycemia, and the loss of this adaptation correlates with a worsening of glucose tolerance.

Correction of hyperglycemia with phloridzin restores the glucagon response to glucose in insulin-deficient dogs: implications for human diabetes

In insulin-deprived alloxan-induced diabetic dogs with severe hyperglycemia and marked hyperglucagonemia, glucagon was not suppressed by intravenous infusion of glucose at a progressively increasing rate up to 24 mg/kg of body weight per min. However, when the hyperglycemia was corrected by phloridzin, a blocker of renal tubular glucose reabsorption, the hyperglucagonemia was readily suppressed by as little as 2 mg of glucose per kg/min. Direct perfusion of phloridzin into the isolated pancreas of nondiabetic dogs had no effect on the in vitro glucagon response to increments in glucose. However, in pancreata isolated from dogs whose glucose levels had been lowered by phloridzin pretreatment, in vitro glucagon suppression in response to glucose increments was more than twice that of controls. This enhancing effect of phloridzin treatment was completely abolished by giving an intravenous infusion of glucose for the 5 hr prior to surgery for isolation of the pancreas. It is concluded that (i) alpha cells have a glucose-sensing system that is independent of insulin and beta cells, and (ii) this system is reversibly attenuated by hyperglycemia. Thus, hyperglycemia, a metabolic consequence of islet cell dysfunction, may be a self-exacerbating inducer of further islet cell dysfunction, a possibility with implications for human diabetes.

Hyperglycaemia as an inducer as well as a consequence of impaired islet cell function and insulin resistance: implications for the management of diabetes

It is postulated that hyperglycaemia influences the natural history of Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes mellitus. Hyperglycaemia, even when mild, can attenuate the secretory response of pancreatic beta and alpha cells to increments in glucose and can impair insulin-mediated glucose transport, thus impeding its own correction and initiating a cycle of progressive self-exacerbation and metabolic deterioration. Both reduced islet function and insulin action may be the consequence of a generalized down-regulation and/or occupation of glucose transporters by hyperglycaemia so that the islets respond less to further increments in glycaemia. The postulated hyperglycaemic cycle can be initiated by any environmental perturbation that increases insulin demand in previously normoglycaemic patients in whom insulin secretion has already reached a maximum level of compensation for peripheral insulin resistance (as in obese pre-Type 2 diabetes) or for a reduced beta-cell mass (as in pre-Type 1 diabetes). Elimination of hyperglycaemia by any means can halt this cycle of progressive metabolic deterioration and may restore transiently metabolic recompensation both in Type 1 and Type 2 diabetes. There is experimental evidence that long-standing severe hyperglycaemia may irreversibly damage beta cells.