The degree of wasting and malnutrition correlates with progression of AIDS. Data from the Multicenter AIDS Cohort Study showed that development of AIDS, fever, thrush, and a CD4 lymphocyte count of less than 100/mm3 were independently associated with continuing loss of body mass. Another study found that measurements of lean body mass, albumin, and transferring predict survival, independent of CD4 count. Starvation causes death when people reach 66% of ideal body weight or 54% of ideal body cell mass; patients with AIDS die at a similar level of weight loss. Because wasting is associated with disease progression, prevention and treatment of wasting should be an integral part of the care of patients infected with HIV. Studies are in progress to document the effect of reversing wasting on disease progression, morbidity and mortality.
Pathophysiology of Wasting:
Not all pathogenetic mechanisms of wasting in HIV have been fully elucidated, but many factors that promote progressive weight loss are understood. Wasting is a product of: perturbations of metabolism and resting energy expenditure caused by the body's immunologic response to HIV and its secondary infections; inadequate nutrition, secondary to poor oral intake, and malabsorption of nutrients, caused by diarrhea and alteration of levels of endogenous anabolic hormones, especially in men.
Perturbations of Metabolism: Resting energy expenditure (REE) increases with HIV infection. Even asymptomatic individuals with early infection have been shown to have an REE of 9% to 12% above seronegative controls. In HIV-associated hypermetabolism, maintenance of body weight requires an increase in caloric intake but, in the absence of OIs, most HIV-positive individuals can maintain adequate intake. Patients with AIDS have REEs of 25% to 34% above controls in some studies, and REE increases even when nutritional intake is poor. Paradoxically, in normal subjects REE decreases when caloric intake declines.
The development of an OI, with its concomitant rise in REE, usually leads to loss of weight, mostly lean body mass. Conversely, weight gain achieved through alimentation alone is mostly adipose tissue. This physiologic preference for fat over lean body mass is more acute in men than women, but all patients with AIDS face a persistent loss of lean body mass that is difficult to replace. The body, instead of reacting to a scarcity of nutrients by preserving lean body mass, combines hypermetabolism with accelerated protein breakdown and negative nitrogen balance to produce wasting.
Limited data are available on the potential role of cytokines in patients with AIDS and more research is needed. However, the mechanism of metabolic dysregulation that inappropriately increases REE and favors adipose tissue over lean body mass may in part be related to the cytokines elaborated in response to HIV and OIs. Tumor necrosis factor (TNF), interleukin (IL) and 6 and interferon alpha, beta, and gamma have all been implicated in metabolic dysregulation. TNF induces weight loss and suppresses appetite in animal models. In addition, these various cytokines may act synergistically to cause futile cycling and inappropriate use of substrates.
Futile cycling of fat occurs in HIV infection, contributing to increased REE as well as hypertriglyceridemia. Peripheral lipolysis releases free fatty acids from adipose tissue. The free fatty acids are re-esterified into triglycerides in the liver and then packaged into very low density lipoproteins (VLDLs), which are released into circulation. The VLDLs are broken down in the periphery by lipoprotein lipase, resulting in storage of the triglycerides in peripheral adipose tissue again. Each of these steps requires adenosine triphosphate (ATP), thus wasting energy, shuttling fat between the periphery and the liver and back again. Current research concludes that TNF, IL-1, IL-6, and interferon alpha play a role in futile cycling of fat.
Inappropriate use of substrate contributes to increased REE and protein wasting seen in HIV. An example of this is the liver utilizing glucose to synthesize triglycerides, instead of protein, in individuals with negative nitrogen balance. This step consumes energy needed to maintain body cell mass. Using energy to make fat is inappropriate in a patient losing body cell mass. The body should be oxidizing fat, not synthesizing it, in this situation. Bodily energy reserves and substrate such as glucose should be employed to restore lean body mass. TNF, IL-1, IL-6, and interferon alpha appear to be involved in the transformation of glucose into triglycerides in the liver.
Malnutrition: Malnutrition occurs in HIV for many reasons. Both illness and inactivity suppress appetite. Many of the medications used to treat HIV and OIs cause anorexia and a variety of GI side effects. Candidiasis, aphthous ulcers, and CMV disease involving the mouth and esophagus make eating difficult and decrease oral intake.
Many secondary infections including MAC, CMV, cryptosporidium, microspora, protozoa, and bacterial pathogens cause diarrhea and secondary malabsorption of nutrients. HIV causes diarrhea through villous atrophy, crypt hyperplasia, lymphocyte infiltration of bowel epithelium, viral infiltration of the mucosae, and the development of an enteric autonomic neuropathy. Many of the well-known hepatic complications associated with HIV, as well as abnormalities of the pancreas caused by ddI, ddC, pentamidine, CMV, MAC, cryptococcus, toxoplasmosis, and TB contribute to diarrhea and malnutrition. Malnutrition is further exacerbated when patients decrease oral intake in an effort to reduce diarrhea.
Androgen Deficiency: One of the roles of androgenic hormones is to help generate and maintain lean body mass. More than half of men with AIDS have low or inadequate androgenic hormone levels due to HIV's interference with the hypothalamus-pituitary axis, adrenal glands, and the testes. Total and free testosterone levels are both suppressed. This lack of endogenous anabolic stimulation is particularly important in light of the metabolic shift away from preservation of lean body mass. HIV's effect on endogenous androgens in women has not been well studied. Given the high prevalence of wasting syndrome in women, both viral effects on female metabolism and the impact of hormone supplementation need further study.
Treatment of Wasting: Optimally, clinicians should try to prevent wasting syndrome as well as treat it when it occurs. Weight loss is often the first sign of a new AIDS-defining illness. Patients should be weighed at every visit and their weight trends recorded on a graph. Because lean body mass is lost in preference to fat, weight alone can be a misleading indicator of nutritional status and clinical course. Laboratory markers of nutritional status include albumin, transferrin, and cholesterol levels. Some clinicians also use bioelectric impedance analysis, which measures lean body mass, to track nutritional status.
Treating Underlying Illness: A crucial first step is to provide appropriate antiretroviral therapy as well as meticulous prophylaxis and treatment of OIs. Two early studies documented clinical and biochemical improvement in individuals treated with AZT monotherapy; one documented an average 2- to 3-kg weight gain and a second demonstrated rapid, significant, and sustained declines in interferon and triglyceride levels in subjects treated with AZT. A later study documented a decrease in REE of 650 kcal/day in patients with CMV colitis who were treated with ganciclovir. Several studies have documented that patients with active, untreated secondary infections are often unable to gain weight even with hyperalimentation.
Patients with untreated secondary infections involving the mouth and GI tract tend to have poor oral intake, since they often have dysphagia and odynophagia as well as diarrhea and malabsorption. Addressing oral and esophageal complications can improve caloric intake and reduce discomfort (see ACC, March 1995 for a complete discussion of esophageal lesions in HIV).
Nutrition: Maintenance of good nutrition is essential. Lost weight can be very difficult to replace. Calorie needs are in the 25 to 60 kcal/kg/day range; 20% should be protein. Working with a nutritionist is helpful. Patients often have deficiencies of micronutrients. One study found a 31% decrease in progression to AIDS in patients taking regular multivitamins with minerals. This finding may be confounded by a bias in favor of more compliant patients with better diets.
Oral feeding is clearly the nutritional route of choice. Emphasizing intake that is high in calories, protein, and fat is important. Over-the-counter nutritional supplements can help patients who are having difficulty with meals, or while they are being treated for oral or esophageal ulcers. Enteral alimentation can be used if oral or esophageal disease or disabling systemic illness makes eating temporarily impractical. Total parenteral nutrition (TPN) has been hotly debated in AIDS. Using TPN in patients with inadequately treated, active OIs and end-stage disease is of little value. Weight gained, if any, will be primarily fat. TPN is occasionally useful as temporary "bridge" therapy for a discrete period during treatment of intercurrent illness. The clear goal should be a restoration of full oral feeding once the patient can eat again. TPN is generally inappropriate in the terminal care of patients with AIDS.