## Core Concept
The question revolves around the management of diabetic nephropathy, a common complication of diabetes mellitus characterized by proteinuria and progressive kidney damage. The goal is to identify a treatment that can attenuate the course of renal disease in a patient with Type 2 diabetes and existing proteinuria.

## Why the Correct Answer is Right
The correct answer, **Angiotensin-Converting Enzyme (ACE) inhibitors**, is supported by evidence showing that these drugs can slow the progression of diabetic nephropathy. ACE inhibitors work by blocking the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor that also promotes sodium retention and fibrosis in the kidneys. By reducing intraglomerular pressure and proteinuria, ACE inhibitors have been shown to slow the decline in renal function in patients with diabetic nephropathy.

## Why Each Wrong Option is Incorrect
* **Option A:** While **Aldosterone antagonists** can be used in certain cases of diabetic nephropathy, especially when there's evidence of resistant hypertension or heart failure, they are not the first-line treatment for attenuating the course of renal disease in diabetic patients with proteinuria.
* **Option B:** **Nonsteroidal anti-inflammatory drugs (NSAIDs)** can actually worsen renal function and are generally contraindicated in patients with diabetic nephropathy and proteinuria, as they can further decrease renal blood flow and increase serum creatinine levels.
* **Option C:** **Thiazolidinediones**, also known as TZDs or glitazones, are used in the treatment of Type 2 diabetes to improve insulin sensitivity but do not have a direct beneficial effect on diabetic nephropathy or proteinuria.

## Clinical Pearl / High-Yield Fact
A key point to remember is that ACE inhibitors or Angiotensin Receptor Blockers (ARBs) are considered first-line treatments for patients with diabetic nephropathy and proteinuria, as they have been shown to reduce the progression of kidney disease. However, they must be used cautiously, especially in patients with bilateral renal artery stenosis or unilateral stenosis in a solitary kidney, due to the risk of acute kidney injury.

## Correct Answer Line
**Correct Answer: D. ACE inhibitors**.